TL;DR
Poor coating uniformity is usually an incorrect spray rate, a blocked spray nozzle, or a pan speed outside the optimum range. Check the spray nozzle and pan speed before adjusting the coating formula.
What you might see
- tablet weight gain variation above specification
- visible color mottling on the tablet surface
- some tablets with bare patches
- spray nozzle partially blocked
Likely causes
Spray nozzle partially blocked altering the spray pattern from a flat fan to a spot
Pan speed too low causing tablets to cascade rather than roll, resulting in uneven exposure
Spray rate too high for the inlet air temperature, causing overwetting and agglomeration
Spray nozzle-to-tablet bed distance set too far, causing spray drying before tablet contact
Required tools
- Analytical balance for tablet weight sampling
- Nozzle cleaning tool
- White paper test target for spray pattern check
Safety first
- Tablet coating suspensions may contain pharmaceutical actives. Wear gloves and a mask when handling coating suspensions to prevent skin absorption or inhalation.
- The coating pan operates at elevated temperature. Allow the pan to cool before opening for nozzle inspection or cleaning.
Procedure
- 1
Sample 30 tablets from the batch at the current coating level, weigh each, and calculate the weight gain CV%. A CV% above 2 to 3% indicates poor uniformity.[1]
- 2
Inspect the spray nozzles by running the spray air without liquid and holding a white paper target at the tablet bed distance. A round or distorted pattern indicates a blocked orifice.
- 3
Clean any blocked nozzle with the prescribed nozzle cleaning tool and appropriate solvent. Do not use a metal probe inside the nozzle orifice.
- 4
Verify pan speed against the batch record. Increase speed slightly if tablets are cascading rather than rolling in a smooth tumble.[1]
- 5
Verify the spray rate and inlet air temperature combination against the process development parameters. Reduce the spray rate if the tablet bed shows moisture.
- 6
Check the nozzle-to-bed distance and adjust to the value on the batch record if it has shifted.
- 7
Continue the batch and repeat the weight gain sampling after coating 5% more weight. Accept only when CV% is within specification.
Sources
Glatt Glatt GC / GMPC Tablet Coating Machine general technical documentation, Glatt
Glatt tablet coating machine general coating process and spray nozzle maintenance (general)
More guides for Glatt Glatt GC / GMPC
How to fix pan drive motor fault on a Glatt GC / GMPC tablet coater
Pan drive faults are usually an overloaded batch, a worn drive belt, or a motor thermal trip. Check the batch weight and drive belt before investigating the motor.
How to fix tablet sticking or picking in a Glatt GC / GMPC tablet coater
Tablet sticking is usually overwetting from too high a spray rate or too low an inlet temperature. Reduce spray rate first, then increase drying air temperature.
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