Working with Rich Packing’s engineers and service specialists, the team reviews content on pharmaceutical packaging equipment using machine specifications, application records, and the company’s 29 years of overseas commissioning and training experience.
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]
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]
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 | Core hardness and pan action | Weak cores or high attrition | Reducing all airflow |
Record when the defect appears, the affected percentage, product temperature, spray rate, pan speed, airflow, and tablet coating-liquid condition. Without records, repeated adjustment can hide the original cause. [1][2]
Sticking occurs when tablets adhere to one another or to the pan because the wet film remains tacky too long. Check spray rate, tablet-bed temperature, airflow, exhaust, and tablet coating viscosity. Reducing spray may help, but poor drying or a tacky formulation can produce the same result.
Picking is local film damage. A wet tablet touches another surface, and part of the tablet coating is pulled away when they separate. It often appears around letters, score lines, or logos. Inspect embossing, core dust, preheating, and the early spray stage.
Twinning means two tablets remain attached, usually face-to-face or along a broad edge. Capsule-shaped, oval, or highly convex tablets are more vulnerable. Check overwetting, pan speed, batch loading, tablet movement, and baffle design. Increasing speed alone may increase edge damage.
Orange peel is a rough, textured film. Droplets may be too large, too viscous, poorly atomized, or partly dried before they spread. Check viscosity, solids content, atomization pressure, gun distance, and product temperature. [1]
Spray drying occurs when droplets lose too much moisture before reaching or spreading over the tablets. Dry particles create dustiness, roughness, weak adhesion, or filled logos. High inlet temperature, excessive atomization, low spray rate, long gun distance, or strong airflow may contribute.
Logo filling occurs when dried or semi-dried tablet coating material collects inside letters, score lines, or embossed details. Check spray drying, solids content, tablet coating build-up, logo depth, and tablet design. Excessive film thickness can make the marking less readable.
Bridging is different from logo filling. The film stretches across a score line or embossed feature and forms a thin bridge. Likely causes include poor film flexibility, excessive film thickness, unsuitable plasticization, weak adhesion, or difficult tablet geometry. [1]
Mottling is uneven color on one tablet, while tablet-to-tablet variation means the batch has inconsistent shade. Causes include poor pigment dispersion, non-uniform spraying, weak mixing, or migration of soluble color during drying. Check suspension agitation, gun output, spray overlap, pan loading, and tablet movement.
Blistering appears as local lifting or bubbling of the film away from the core. It is often associated with poor adhesion, trapped moisture, or rapid heating. Review preheating, product temperature, curing, core moisture, and film adhesion.
Film cracking occurs when the tablet coating cannot tolerate stress from drying, handling, or changes in the core. Possible causes include insufficient plasticizer, a brittle polymer, excessive film thickness, rapid drying, core expansion, or impact. Note whether cracks appear immediately or after storage. [1]
Peeling is the separation of a larger film section from the tablet. Dust, excess surface lubricant, low film strength, poor plasticization, overheating, or core erosion can contribute. A tablet deduster can remove loose powder, but it cannot correct an unsuitable formulation or over-lubricated core. [1][2]
These defects all involve material loss. Chipping affects edges, pitting forms small depressions, and surface erosion creates broader worn areas. Check core hardness, friability, moisture, pan speed, baffle contact, batch size, and spray wetting. Weak cores may survive discharge from the rotary tablet press machine but fail under repeated movement in the tablet coating pan.
A stable process begins with a coat-ready core. Tablet hardness must be sufficient for loading, tumbling, spraying, and discharge, but hardness alone does not guarantee success. A tablet can be hard yet have weak edges, internal stress, high friability, or poor surface adhesion.
Core porosity affects wetting. Porous tablets can absorb liquid quickly, while dense or heavily lubricated surfaces may resist adhesion. Excess hydrophobic lubricant at the surface can weaken the film-core bond. Shape also matters: deep concavity, narrow score lines, sharp logos, and capsule-shaped tablets can increase twinning, bridging, and picking. [2]
Consistent tablet compression on the rotary tablet press machine helps control hardness, thickness, and surface condition. Dust should be removed before tablet coating. A tablet deduster supports surface cleanliness, but it does not replace correct granulation, tablet compression, or core formulation.
Do not adjust every parameter together. Start with the variables that control wetting, evaporation, and tablet movement:
1. Product temperature
2. Spray rate
3. Atomization pressure
4. Pattern air
5. Inlet and exhaust airflow
6. Pan speed
7. Gun distance and angle
8. tablet coating-liquid solids and viscosity
| Parameter | Too low | Too high | Defects often seen |
|---|---|---|---|
| Spray rate | Slow build or poor coverage | Overwetting | Roughness or sticking |
| Atomization pressure | Large droplets | Premature drying | Orange peel or spray drying |
| Product temperature | Slow evaporation | Poor spreading | Sticking or rough film |
| Pan speed | Weak mixing | High attrition | Color variation or chipping |
| Airflow | Moisture builds up | Surface dries too quickly | Sticking or spray drying |
Product temperature describes the tablets more directly than inlet temperature alone. Spray dynamics also depend on solids content, viscosity, atomizing air, pattern air, gun distance, and process airflow. Changes in spray rate, airflow, humidity, and drying conditions can alter both the tablet-bed environment and the likelihood of tablet coating defects. Change one major variable, allow the process to stabilize, and record the result. [2]
Investigate the machine when a defect follows a spray gun, air zone, or repeated operating pattern. Warning signs include unequal gun output, blocked nozzles, unstable pan speed, inaccurate temperature readings, weak exhaust control, poor spray overlap, or baffles that do not move the tablets evenly.
A suitable tablet coating suspension can still produce mottling, roughness, or overwetting if one gun delivers a different rate or angle. Cleaning residue may restrict nozzles, while unstable air handling can move product temperature outside the intended range. Maintenance should include nozzle inspection, sensor calibration, airflow checks, and confirmation of pan sealing and negative-pressure control.
Rich Packing integrates equipment R&D, production, and sales within one manufacturing system. Its 6S-managed production process includes quality checks covering raw-material procurement, component handling, assembly, and final equipment testing, helping maintain consistency in critical tablet coating machine functions such as pan drive, spray delivery, airflow control, and temperature monitoring.
tablet coating defects should be investigated through the core, tablet coating formulation, spray and drying conditions, and machine setup. Sticking, twinning, orange peel, cracking, peeling, and color variation may look different, yet several can share the same imbalance between wetting, evaporation, adhesion, and tablet movement.
A practical investigation starts with the visible defect, checks the most likely root-cause group, and changes one major variable at a time. Stable coated-tablet quality depends on coat-ready cores, a suitable formulation, controlled parameters, and a tablet coating machine that delivers repeatable spraying, airflow, and tablet movement.
Common defects include sticking, picking, twinning, orange peel, spray drying, logo filling, bridging, mottling, blistering, cracking, peeling, and edge or surface erosion.
Common causes are excessive spray rate, low product temperature, insufficient airflow, poor exhaust, or a formulation that remains tacky too long.
Orange peel usually results from poor droplet spreading. High viscosity, weak atomization, large droplets, long gun distance, or rapid surface drying can create the rough texture.
Check tablet shape, overwetting, pan speed, batch loading, and baffle design. Oval or capsule-shaped tablets may need a movement pattern that separates flat surfaces more effectively.
Sticking means tablets adhere to each other or equipment. Picking occurs when they separate and pull away part of the wet tablet coating or tablet surface.
Yes. Weak, friable, or stressed cores can chip, erode, crack, or peel. Review hardness together with friability, edge strength, moisture, and tablet compression consistency.
Start with product temperature, spray rate, atomization, airflow, pan speed, and gun position. Change one major variable at a time and record the result.
No. Equipment improves spray control, airflow, mixing, and repeatability, but defects can also originate from core design, formulation, moisture, lubricant level, or tablet coating-liquid properties.
1. Zaid, A. N. et al. A Comprehensive Review on Pharmaceutical Film tablet coating.National Library of Medicine — PMC Open source https://pmc.ncbi.nlm.nih.gov/articles/PMC7605601/
2. Porter, S. C. How to Prevent tablet coating Problems. Pharmaceutical Technology.Read the article Open source https://www.pharmtech.com/view/how-prevent-tablet-coating-problems
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