Tablet coating defects & Reasons

Tablet coating is an science of coating edible paint over uncoated tablet to achieve specific benefits during coating technicians come across various problems we will discuss further in article

Poor weight gain in tablets during coating operation is due to

• High atomisation air is breaking coating solution into very fine liquid droplets which are distributed unevenly on tablet bed.
• High exhaust bed temperature is not allowing the coating solution uniformly on tablet bed some part of solution is dried before reaching tablet bed.
• High nozzle to bed distance is not allowing coating solution to deposit uniformly due to air turbulence
• High spray drying will dry the solution before it reaches tablet bed thereby poor weight gain
• Friable tablets also leads to poor weight gain as the tablets will break in pan and solution is wasted on them.

Color variation in tablets during coating operation is due to

• Poor mixing of coating solution is done prior to coating.
• Overlapping spray is occurring during process due to spray pattern not checked properly.
• Uneven droplet size of spray due to problem or jam in atomisation air nozzle.
• Spray deviation during process due to unnecessary change in inlet or exhaust air volume.
• Gun geometry setup not done properly.
• High spray rate will also leads to color variation.
• Unnoticed choke in spray gun.

Twinning of tablets during coating operation is due to

• High spray rate is over-wetting the tablet
• Overlapping of spray.
• Atomisation air is low and the coating solution is not dispersed in fine particles
• Exhaust temperature is low to dry the coating solution and twinning occurs.
• Nozzle to bed distance is low leading to over wetting of tablet and finally twinning.

Rough surface of tablet during coating is due to

• Turbulence in air flow.
• Spray pattern is poor.
• Concentration of solid is high.
• Hardness of tablet is low.

Picking occurs during coating due to

• Low bed to nozzle distance is there so,excess of spray is overwetting the tablet leading to picking.
• Low exhaust bed temperature is not drying the tablet bed uniformly leading to picking.
• Air bubbles are present in solution.
• Atomisation air is not uniform or jam in spray gun.
• Pan speed is too low.

Film cracking during coating

• Core of tablet swells due to moisture absorption.
• Drying not proper.
• Poor tensile strength of film.

Film chipping

• If pan RPM is high it leads to chipping.
• Sharp edges of tablets also leads to chipping.
• Low spray rate.
• Mechanical stress on tablets is high.

Film peeling

• Smooth surface of tablet leads to peeling.
• Adhering property of polymer used is poor.

Bridging and logo filling

• High spray rate leads to logo filling and bridging.
• Concentration of solids is more in coating solution.
• Tablets breaks during coating in pan.
• Atomisation air is low.