Troubleshooting Guide – TOP 10

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.

The top 10 mistakes:

1. Orange Peel / Roughness

Tablet with a rough coating.

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)

Remedy:

  • Increasing the spray rate
  • Decreasing the drying capacity
  • Reducing the atomizing air pressure
  • Decreasing the viscosity
  • Optimizing the distance between nozzle and tablet bed

2. Logo Bridging

two pink tablets - 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)

Remedy:

  • Decreasing the viscosity
  • Increasing the plasticizer content
  • Reducing the spray rate
  • Adjusting the spray pressure (increase or decrease)

3. Twinning

Two Yellow Pills Stick Together.

Two or more tablets stick together.

Possible Reason:

  • Overhumidifcation
  • Process air volume is too low
  • Tablet shape “planar” is not suitable

Remedy:

  • Reducing spray rate
  • Increasing the drying capacity
  • Optimizing the form of the tablets to “biconvex”
  • Using release agents in the formulation

4. Sticking and ripping off coating

tablet with ripped 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 damp

Remedy:

  • Increasing the pan speed
  • Increasing the inlet air temperature
  • Increasing the process air volume
  • Reducing the spray rate

5. Scuffing

Troubleshooting Guide – Scuffing.

Gray layer forms on the tablet surface.

Possible Reason:

  • Titanium dioxide quantity is too high
  • Interaction between drum wall and coating

Remedy:

  • Reducing the titanium dioxide
  • Spraying the drum prior to the trial

6. Capping

How to solve capping?

Detachment of the film surface.

Possible Reason:

  • Hygroscopic core
  • Disintegrants are used

Remedy:

  • Using a subcoat
  • Optimizing process parameters

7. Color variation I

Color Variation. Different shades of Blue on several pills.

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

Remedy:

  • Increasing the coverage properties of the coating (more pigments)
  • Reducing the solid content
  • Increasing the weight gain level

8. Color variation II

BIOGRUND - Bad Tablet

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

Remedy:

  • 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

9. Peeling

Peeling Example

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

Remedy:

  • Using a subcoat
  • Increasing the plasticizer content
  • Spraying with drier conditions
  • Increasing the film forming polymer

10. Friability

Tablet mass reduced due to abrasion.

Possible Reason:

  • Mechanical stress
  • Tablets are too soft
  • Tablets are too damp
  • Pan speed is too high

Remedy:

  • Reducing the pan speed
  • Optimizing the core formulation
  • Spraying with drier conditions
  • Using the interval “jog mode” while heating cores

Extra Info:

You can download the complete white paper and the brochure of the Troubleshooting Guide here.

Do you have other problems with the coating process or need more tips to avoid errors?
Contact us.