The tablet pan may seem like a basic component of a coater, but its size and shape affects coating uniformity as well as the
number of defects in a batch, and it plays an important role in increasing process efficiency.
Traditional tablet pans are short in length and large in diameter as shown in Figure 3a. This geometry leads to thick tablet
beds. A zone in the middle of the traditional thick tablet bed, however, is slow moving, and tablets in that area do not get
exposed to the surface of the bed as often. High-efficiency coaters, in comparison, have coating pans that are longer in length
but smaller in diameter, as shown in Figure 3b.
Figure 3: (a) A traditional tablet-coating pan is shorter in length and larger in diameter than a (b) high-efficiency coating
Figure 4a shows the slow-moving zone in the traditional tablet pan. In the high-efficiency coater, shown in Figure 4b, the
tablet bed is spread wider, and there is no slow-moving zone. The tablets are in constant motion, so they enter the spray
zone more often, which results in better coating uniformity and improves efficiency because less coating solution is wasted
and thus less time is required compared to a traditional tablet bed.
Figure 4: The tablet bed is thicker in (a) a traditional coating pan and has a slow-moving zone not found in (b) a high-efficiency
The smaller diameter pan also helps prevent twinning (i.e., tablets sticking together in the tablet bed). These tablets must
be sorted out and often are counted as rejects, thus affecting overall batch efficiency.
High-efficiency tablet coaters improve efficiency by reducing waste of coating material through eliminating spray drying.
Traditional tablet coaters send airflow from the top or side of the coater, across the spray zone, through the tablet bed
and out (see Figure 5). Bringing hot air into direct contact with spray as it is airborne, however, will dry part of the
solution before it hits the tablet surface.
While running a conventional coater, one can see a cloud-like effect where the coating spray meets turbulent air, which spreads
the solution out and causes it to cover the pan and spray arms instead of the tablets. This wastes coating material and causes
loss of tablets when they stick to the pan or get trapped in the machine's filter system.
Figure 5: Air flow in a conventional coating process enters from the top or side.
With advanced coating technology, airflow enters the coater from beneath the tablet bed, and it is distributed over the entire
length of the pan as shown in Figure 6. All airflow through the tablet bed is in the direction of flow, leaving no hot air
in the spray zone and making spray drying almost non-existent. In addition to eliminating spray drying on the pan and spray
arms, the lack of hot air in the spray zone ensures that droplets are wet when they hit the tablet surface. When airflow partially
dries a droplet of coating material, it has a tendency to bead on the table pan instead of disperse on the tablets. Wet droplets,
however, disperse well and so require less coating solution to achieve coating uniformity.
Figure 6: Air flow in a high-efficiency coating process enters from beneath the tablet bed.
Manufacturers want to increase the length of campaigns (i.e., the number of batches run continuously). Because high-efficiency
coaters reduce the amount of wasted coating solution left on the tablet pan and spray arms, manufacturers can run a campaign
longer without stopping to clean.
Less cleaning also helps reduce wash water use and improve waste management. A typical coater wash cycle uses 400 gallons
of water. Because newer coaters require fewer cleanings, manufacturers potentially can save thousands of gallons of water
and reduce wastewater processing each month.
All coaters have dust collectors or filter systems to catch solidified solution that is lost during processing. Since high-efficiency
coaters lose less solution than conventional coaters, filters can be changed less often, thus saving time and cost of maintenance
as well as the cost of expensive filters.
In conclusion, advanced tablet coating technologies offer advantages that can lower the cost per tablet and increase processing
efficiency, yielding a significant return on investment for manufacturers.
Martin Hack Martin Hack is the vice president and general manager of L.B. Bohle, 700 Veterans Circle, Suite 100, Warminster PA, 18974,
tel: 215.957.1240, firstname.lastname@example.org