Tablet Coating Problems in Pharma Manufacturing : How to Solve

Coating problems occurs during manufacturing of tablets in Pharma industries

Tablet Coating Problems in Pharma Manufacturing : How to SolveIn this article, we will discuss various coating problems occurs during manufacturing of tablets in Pharma Industries. We will also discuss the possible reasons and their solutions to avoid such defects to achieve the quality products which should be free from defects.



Blistering is detachment of film from the substrate and it forms blister.

Possible reasons:

Overheating, either during spraying or at the end of the coating run, this overheating affects elasticity strength and adhesion of the film.

Solutions: Milder the drying conditions.


Film becomes chipped and dented, usually at the edges of the tablet

Possible reasons:

This is because the too much attrition during coating process.


  • Decrease speed of rotation of the drum or fluidizing air in pan.
  • Increase film hardness by increasing the molecular grade of polymer.


When film cracks across the crown of the tablets is called cracking. When film splits around the edges of the tablet is called Splitting. It happens when internal stress of the film is more than tensile strength of the film.

Possible reasons:

  • Use of high molecular weight polymers or polymeric blends.
  • Insufficient or improper concentrations of plasticiser or pigment.
  • Different thermal expansion characteristics of core and coating.


  • Select and adjusting proper plasticizer or Pigment type and concentration
  • Use lower molecular weight polymers or polymeric blends.
  • Avoid mineral types of fillers.



When the upper or lower part of the tablet separates, either partially or completely from the tablet and comes off as a cap, during ejection from the tablet press, or during subsequent handling. It happens due to the air-entrapment in a compact during compression process or because of tablet expansion during ejection of a tablet from a die.

Possible reasons:

  • Low moisture content.
  • Inadequate drying of granules.
  • Too much fines in the granulation.
  • Inadequate amount or not proper type of binder.
  • Inadequate amount or not proper type of Lubricant.
  • High speed of turret
  • Seep –off blade not adjusted properly.
  • Improper setting of lower punch.


  • Increase moisture content of granules by adding hygroscopic martial like PEG, sorbitol etc.
  • Ensure proper drying of granules
  • Remove excess fines from granules
  • Adjust adequate amount or change type of binder.
  • Adjust adequate amount or change type of Lubricant.
  • Adjust speed of turret.
  • Adjust Seep –off blade properly.
  • Ensure proper setting of lower punch.


Picking and Sticking:

When coating removes a piece of the tablet from the core, it happens sometime when tablets sticks together.

Possible reasons:

  • Inefficient drying.
  • Over wetting, due to high spray rate of coating solution or too low pan speed.
  • Improper distribution of coating liquid.


  • Improve drying conditions.
  • Adjust proper spray rate and pan speed to avoid over wetting.
  • Adjust proper viscosity of coating solution to ensure proper distribution of coating solution.


Color Variation:

It involves variation of color of film.

Possible reasons:

  • Inadequate coating
  • Improper mixing during coating
  • Poor spray pattern
  • Migration of dyes during drying.


  • Adjust and ensure proper coating.
  • Increase pan speed to ensure proper mixing.
  • Adjust gun position and ensure optimum number of guns to cover the tablet bed properly.
  • Adjust plasticizers type and concentration, reduce drying temperature.



Uneven distribution of color on a tablet, with light or dark spots.

Possible reasons:

  • Inadequate mixing of colored binder solution.
  • Migration of dye to the granule surface during drying.
  • When drug substance is colored and Excipients are white or colorless.


  • Ensure proper mixing of colorant and adhesives.
  • Reduce drying temperature, change binder or solvent system.
  • Use suitable colorants



When two tablets sticks tighter. It usually happens with capsule shaped tablets.

Possible reasons:

  • High spray rate and low pan speed.
  • Low distance between spray guns and tablets bed.
  • Inappropriate shape of tablets.


  • Reduce spray rate and increase pan speed.
  • Increase distance between spray guns and tablets bed.
  • Slight modification in design of tooling.

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