10 Errors that can occur during the coating process and how to avoid them
Many parameters must be considered before and during the coating process. Sometimes it is necessary to adjust parameters to get the best possible result.
The correct and precise choice of process parameters is crucial for a flawless result and an optimal coating. Various influencing factors can lead to useless coating results. If the tablet is too soft or the tablet shape has been chosen incorrectly. But also a too low air pressure or a too high spray rate can lead to unwanted results. To avoid this and to optimize the coating process, many changes can be made.
In the BIOGRUND Troubleshooting Guide you will find possible reasons and solutions for the respective problem, which will make your troubleshooting easier and faster.
Orange peel / Roughness.
Rough or uneven surface of the tablets.
Possible reason:
- Distance between nozzle and tablet bed is incorrect
- Spray angle is wrong
- Spray drying
- Sedimentation of the dispersion
- Viscosity/solid content is too high
- Core properties are inadequate (high friability)
- Atomizing air pressure incorrect – too high or too low (AA)
Solution:
- Increasing the spray rate
- Decreasing the drying capacity
- Reducing the atomizing air pressure
- Decreasing the viscosity
- Optimizing the distance between nozzle and tablet bed
Logo bridging.
Filling of the logo or the break line.
Possible reason:
- Viscosity is too high
- Plasticizer content is too low
- Spray rate is too high
- Atomizing air pressure is not right (too low or too high)
Solution:
- Decreasing the viscosity
- Increasing the plasticizer content
- Reducing the spray rate
- Adjusting the spray pressure (increase or decrease)
Twinning.
Z
Two or more tablets stick together.
Possible reason:
- Overhumidifcation
- Process air volume is too low
- Tablet shape “planar” is not suitable
Solution:
- Reducing spray rate
- Increasing the drying capacity
- Optimizing the form of the tablets to “biconvex”
- Using release agents in the formulation
Sticking and ripping off coating.
Tablets rip off the coating from each other.
Possible reason:
- Pan speed is too low
- Air temperature is too low
- Process air volume is too low
- Spray rate is too high
- Process is too dam
Solution:
- Increasing the pan speed
- Increasing the inlet air temperature
- Increasing the process air volume
- Reducing the spray rate
Scuffing.
Gray layer forms on the tablet surface.
Possible reason:
- Titanium dioxide quantity is too high
- Interaction between drum wall and coating
Solution:
- Reducing the titanium dioxide
- Spraying the drum prior to the trial
Capping.
Detachment of the film surface.
Possible reason:
- Hygroscopic core
- Disintegrants are used
Solution:
- Using a subcoat
- Optimizing process parameters
Color variation I.
Batch has heterogeneous color.
Possible reason:
- Coverage properties of the coating are insuffcient
- Solid content of the suspension is too high
- Weight gain level is too low
- Batch quantity is too low
Solution:
- Increasing the coverage properties of the coating (more pigments)
- Reducing the solid content
- Increasing the weight gain leve
Color variation II.
Individual tablets have heterogeneous color.
Possible reason:
- Application rate is too low
- API interacts with the coating material
- Low opacity
- Active ingredients diffuse from the core
- Overhumidifcation
Solution:
- Increasing the weight gain
- Adapting the formula or changing the pigments
- Increasing the coverage properties of the coating formulation
- Using a subcoat
- Increasing the tablet bed temperature
Peeling.
Spalling of the film – possible cracking of the coating.
Possible reason:
- Tablet is swelling
- Plasticizer content in coating suspension is too low
- Tablet is too wet
- Tablet hardness is too low
- Tablet is outgassing
Solution:
- Using a subcoat
- Increasing the plasticizer content
- Spraying with drier conditions
- Increasing the film forming polymer
Friability.
Tablet mass reduced due to abrasion.
Possible reason:
- Mechanical stress
- Tablets are too soft
- Tablets are too damp
- Pan speed is too high
Solution:
- Reducing the pan speed
- Optimizing the core formulation
- Spraying with drier conditions
- Using the interval “jog mode” while heating cores
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