Orange Peel Tablet Coating Defect

Tablet coating is a process in which we apply a thin layer of polymer over the tablet surface for environmental protection & to achieve various other desired effects like taste masking, delayed release, etc. The coating process may vary from as short as 02 hours to as long as many hours depending on the type of coating, coating formulation & batch size.

The coating process does not run as smoothly as we think; rather, we may face different problems or defects during the coating process.These problems may be related to the core tablet properties, defects in tablet coating formulation or the processing parameters of the coating equipment.

In this article, we are going to discuss a specific tablet coating defect which is known as Orange Peel Effect or orange peel tablet coating defect.

If you want to read details of the coating process & processing parameters then check the following.

Read Details

Basis of Tablet Coating.

Technical Aspects of Tablet Coating Process.

Let’s start with our main topic, which is the Orange Peel Effect.

What Is the Orange Peel Effect?

The Orange Peel effect is the tablet coating defect where the tablet surface is not smooth rather it is rough, non-glossy, porous & resembles the skin or peel of the orange.

The orange peel effect is also known as excessive roughness & due to its resemblance with the peel of an orange, it is known as orange peel effect or orange peel tablet coating defect

Explanation

In the routine coating process, the tablet surface is smooth, glossy & shiny during the coating process but sometimes the tablet surface starts to become rough & it has a matte finish. This defect is known as Orange Peel or excessive roughness.

Reasons & Remedies Of the Orange Peel

The orange peel tablet coating defect may be due to the following main reasons

Core Tablet Properties
Defects In Tablet Coating Formulation
Variations In Processing Parameters

Core Tablet Properties

If the core tablet formulation is not properly designed or the hardness of the tablet is low it may result in softening of tablets after the application of the spray.

If tablets become soft the surface roughness or orange peel defect is observed with further processing.

Solution

The core tablet formulation & hardness must be robust to withstand the coating process without surface roughness.

Defect In Tablet Coating Formulation

The orange peel defect is also observed with those tablet coating formulations where the viscosity of the coating suspension is very high.

Coating suspension may be viscous due to less quantity of solvent or more quantity of solid contents.

Due to high viscosity, this coating solution is not uniformly spread over the tablet surface & after drying it results in an uneven & rough surface that looks like a peel of an orange.
Due to the high viscosity of coating suspension, it is not properly automized.
Highly viscous coating suspension is not properly sprayed at a low spray rate & solvent is evaporated due to rapid heat resulting in the accumulation of solid particles over the tablet surface & give a non-glossy or matt appearance.

Solution

Decrease the viscosity of the tablet coating formulation by adding more solvent.
Decrease Viscosity by decreasing the solid content if possible.
Increase atomisation pressure to properly sprinkle the droplets over tablets.
The spray rate can be increased to avoid rapid evaporation.

Variations in processing parameters

The orange peel defect during the tablet coating process may also be observed due to an imbalance of coating processing parameters which may result in conditions like overwetting & results in orange peel defect.

Tablet Over-wetting

If we talk about the processing parameters then overwetting is the main reason for tablet excessive roughness or orange peel coating defect.

Let’s discuss which are the processing parameters that may result in tablet overwetting during the coating process.

Humidity Of Pan

If the environment inside the coating pan is more humid or inlet air has a higher humidity level, it will result in over wetting of tablets.

Due to over wetting of the tablets, film on the tablet surface rubs with each other & it becomes rough like the orange peel.

Solution

Avoid a humid environment inside the coater & for this use processed inlet air & open the exhaust air opening for an optimized level.
Increase the inlet air temperature to properly dry the tablets.

Spray Gun To Tablet Bed Distance

If the spray gun to tablet bed distance is decreased it may result in over-wetting of the tablets & orange peel is observed.

Solution

Increase the distance between spray guns and tablet bed.

Spray Gun To Spray Gun Distance

If the distance between spray guns is less it will result in tablet over wetting due to spray overlapping which may result in orange peel.

Solution

Adjust the distance between spray guns in such a way that no overlapping of spray occurs.

Spray Guns Blockage

If spray guns are not properly working & one or two guns are blocked it may result in localized over wetting & may develop tablet roughness or an orange peel effect.

Solution

Ensure smooth running of all spray guns.

Inlet Air Temperature/Air Volume

If tablets are not properly warmed during the coating process due to less inlet air temperature or less airflow then tablets will become over wet & result in an orange peel tablet coating problem.

Solution

Increase the inlet air temperature & airflow volume.

Pan Speed

If the pan speed is very low & spray rate is high it will result in over wetting, due to increased dwell time.

Solution

Increase the pan speed to reduce the dwell time.

Atomization Air Pressure

If atomization air pressure is very high & tablet bed temperature is low it will hit the tablet surface with high velocity & result in tablet roughness or orange peel defect.

Solution

Reduce the atomization air pressure

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