Coating - Key elements to tablet film coating - These are the must haves!
- Consistent Tablet hardness is step one, good coating is next to impossible without consistent hardness (the wider the range the greater the variation) ….soft tablets erode easily and hard tablets do accept the solution and the coating wants to peal.
- Pre-heating or coating the inside of the pan will prevent “marking”
- Loading the pan in the correct position so tablets do not hit the baffles and anti-slide bars is a must to prevent chipping and breakage.
- Jog or slow tumble to dedust tablets (cores) before spraying. Dust and tablet flash (crowning, extrusions) must be eliminated or it could ruin the entire batch. The defect is picking…whereby dry particles pull coating away from tablet to tablet….so a small problem grows and could ruin the entire batch.
- For most film coatings the product bed temperature must be maintained above 42°C…typically 45°C is a sweet spot. If temperatures are too low the coating will not dry quickly and could result in sticking, if temps are too high the coating will dry too quickly and not adhere to the table surface.
- Start slow: in the beginning the “pan rpm” should be slow, just quick enough to have good even flow (no stalling). This is dependent on tablet size, shape, and hardness. So typical speeds are in the area of 2-4 rpm.
- Spraying the solution: to begin with the guns should be clean, needles are straight and lubricated, seals are clean and not damaged. Check to make sure all guns are spraying within a range of ±10ml. Set guns about 8-10 from the tablet bed surface and make sure the atomizing air provides a spray that will dry on contact with the tablets.
- Tablet / spray exposure: the idea is to have the spray dry immediately after it reaches the tablet. As the tablets tumble and flow they get exposed to a slight mist that dries quickly. If the tablets are exposed to too high of spray rate they might stick to other tablets or to the coating pan surface. Once the tablets are covered they are now protected and not a vulnerable to pan speeds and spray rates. (coatings make the tablet stronger), then the pan rpm can be increased and the spray rates can be increased.
- Once the desired amount of coating is complete the spray and heat are turned off. The pan rpm is reduced to a very slow rotation so the tablets can cool to ambient temp. Unloading hot tablets can result in sticking and moisture buildup.
- Unload carefully, tablets are tougher now but still subject to breakage from poor handling.
- Make sure the coating pan and inlet/ exhaust plenums are CLEAN and DRY.