Tablet Coating Defects: 12 Common Problems and Practical Fixes
Tablet coating defects can affect more than appearance. A rough film, unreadable logo, cracked surface, or uneven color may indicate poor adhesion, unstable drying, weak tablet cores, or inconsistent spraying. Some defects are cosmetic, while others may affect identification, handling, moisture protection, or the expected performance of the coated tablet. Troubleshooting works best when the defect is treated as evidence rather than a diagnosis. The same visible problem may come from the tablet core, tablet coating formulation, spray system, drying conditions, or movement inside the tablet coating machine. The investigation should identify the defect, check the most likely variables, and change one major factor at a time. [1][2] What Are tablet coating Defects? tablet coating defects are unwanted changes in the film, color, surface, edge, logo, or physical condition of a tablet during or after tablet coating. They may appear during spraying, drying, curing, discharge, or final inspection. They are not always the same as tablet compression defects. Capping, lamination, weak edges, or high friability may begin during tablet compression. tablet coating can make these weaknesses more visible because tablets are exposed to heat, moisture, repeated movement, and contact with other tablets. Before changing the tablet coating recipe or machine settings, inspect uncoated cores from the same batch. Check hardness, friability, dust, moisture, shape, embossing, and surface condition. This helps separate defects created during tablet coating from problems carried into the process. [2] What Should You Check Before Adjusting the tablet coating Process? Place the problem into one of four groups: 1. Tablet core quality: hardness, friability, porosity, moisture, dust, shape, or weak edges. 2. tablet coating formulation: polymer, plasticizer, solids content, viscosity, pigment dispersion, or adhesion. 3. Spray and drying conditions: spray rate, atomization, gun distance, inlet air, exhaust, and product temperature. 4. Equipment setup: gun alignment, baffles, pan speed, airflow balance, sensors, and control stability. The defect name alone does not reveal the root cause. Sticking may result from excessive spray, insufficient drying, a tacky formulation, or low product temperature. Cracking may come from a brittle film, an expanding core, or mechanical stress. Defect pattern First check Likely cause Avoid doing first Tablets stick together Product temperature and spray rate Overwetting or slow drying Raising heat sharply Surface is rough or dusty Atomization and gun distance Spray drying or large droplets Increasing spray rate Film cracks or peels Core condition and film flexibility Poor adhesion or excessive stress Changing pan speed only Color is uneven Spray pattern and tablet mixing Poor distribution or pigment migration Adding more pigment Edges chip or erode ...