Tablet Coating Defects: 8 Common Issues & Proven Fixes for Pharma Manufacturing

Tablet coating is a critical yet complex step in pharmaceutical manufacturing. Even minor process deviations can lead to defects, affecting product quality and efficiency. This guide outlines the most common coating issues, their root causes, and practical solutions to ensure optimal performance.

1. Uneven Coating (Inconsistent Film Thickness)

Possible Causes:

• Incorrect spray gun settings (pressure, nozzle position)

• Poor atomization of coating solution

• Inconsistent pan rotation speed

• Non-uniform tablet bed movement

Solutions:

• Adjust spray gun: Optimize pressure, nozzle angle, and distance from the tablet bed.

• Improve atomization: Ensure fine mist formation by adjusting air pressure and viscosity.

• Optimize pan speed: Adjust rotation to enhance tablet mixing and coating distribution.

2. Orange Peel Effect (Rough Surface Texture)

Possible Causes:

• Spray drying (droplets dry before reaching tablets)

• High coating viscosity

• Inadequate inlet air temperature

• Poor atomization

Solutions:

• Increase spray rate to reduce premature drying.

• Lower viscosity by adjusting solvent ratio.

• Optimize drying conditions (increase air temperature if too low, reduce if too high).

3. Tablet Sticking (Twinning or Pan Adhesion)

Possible Causes:

• Excessive spray rate → over-wetting

• Low pan speed → poor tablet movement

• High humidity in the coating chamber

• Unsuitable tablet shape (e.g., flat surfaces prone to sticking)

Solutions:

• Reduce spray rate to prevent over-wetting.

• Increase pan speed for better tablet movement.

• Use anti-sticking agents (e.g., talc, magnesium stearate).

• Switch to biconvex tablets (if possible) to minimize contact points.

4. Chipping and Edge Defects

Possible Causes:

• Weak tablet cores (low hardness)

• Improper spray angle (edges not coated properly)

• High pan speed causing mechanical abrasion

Solutions:

• Optimize spray angle to ensure full edge coverage.

• Increase tablet hardness in core formulation.

• Reduce pan speed if abrasion is observed.

5. Color Variation (Batch or Tablet-Level Inconsistency)

Possible Causes:

• Poor pigment dispersion in coating suspension

• Low opacity of coating material

• API-core interaction affecting color

• Insufficient coating weight gain

Solutions:

• Increase pigment concentration for better coverage.

• Ensure uniform mixing of coating suspension.

• Apply a subcoat to prevent API interference.

• Adjust spray rate & drying for consistent film buildup.

6. Film Cracking or Peeling

Possible Causes:

• Low plasticizer content → brittle film

• Rapid drying → stress cracks

• Tablet swelling (moisture absorption)

Solutions:

• Increase plasticizer in coating formulation.

• Optimize drying conditions (avoid excessive heat).

• Use a subcoat to improve adhesion.

7. Blistering (Bubble Formation on Coating)

Possible Causes:

• Too high inlet air temperature → rapid drying

• Excessive spray rate → trapped moisture

Solutions:

• Reduce spray rate to allow proper drying.

• Lower inlet air temperature for gradual film formation.

8. Logo Bridging (Filling of Engravings)

Possible Causes:

• High coating viscosity

• Low atomizing air pressure

• Excessive spray rate

Solutions:

• Reduce viscosity (adjust solvent ratio).

• Increase atomizing air pressure for finer droplets.

• Optimize spray rate to prevent over-application.

Conclusion

By understanding these coating defects and their solutions, pharmaceutical manufacturers can significantly improve production efficiency and tablet quality. As a leading manufacturer of high-precision tablet coating machines, LTPM designs equipment with advanced features to prevent these common issues. Contact us to see how our technology solves your toughest coating challenges.