Issue link: https://www.e-digitaleditions.com/i/1287521
12 September 2020 Tablets & Capsules For minitablets, use tight tolerances for the lower punch's working length to minimize variations in fill. An extended-length feeder can provide more time for the formulation to flow into the small die bores of microtip tooling. Often a simple gravity feeder can be advantageous for limiting the amount of formulation in the feeder. With power feeders, a reduced-volume hopper design is best. Consider installing a feeder restrictor plug to block the feeder's first opening. Because minitablets require less formulation than standard tablets, reducing the paddle speed is advisable. Reducing the hopper vol- ume can also be beneficial because the total amount of material needed for a batch is often lower for minitablets than for standard tablets, and the formulations tend to be more expensive. Depending on your formulation's characteristics, min- imize the clearance between the feed pan and the die table during setup. Generally, heat-sensitive formulations need more clearance and formulations with high percent- ages of fines need less clearance. Verify the turret face runout since proper feed-pan clearance depends on a die table that doesn't rise and fall excessively as it rotates. Have the tablet press serviced if needed. To avoid overfilling the feeder chamber, choose a feeder with a metering capability that uses a combination of sensors and a vibrator to convey the desired amount of formulation. The amount of clearance between the punch tip and the die bore wall can affect the vacuum pres- sure. Reduce this clearance by 0.005 to 0.008 millimeter (0.0002 to 0.0003 inch) to increase vacuum pressure, par- ticularly for formulations with a bulk density below 0.5 gram per milliliter. Tablet ejection Perhaps the most common issue related to minitab- let production is tablet damage during ejection. Small tablets have thinner side walls than large tablets, and as a result, are more sensitive to the takeoff plate's height and location. Proper height and placement of the tablet stripper is necessary to maintain a smooth, stable path off the press. Often you will need to move the tablet stripper slightly forward and closer to the die plate for minitab- lets. Improper setting of the ejection height and incorrect overall lengths for the lower punches can introduce insta- bility in the tablet stream at takeoff, resulting in chipped or broken tablets and potentially damaging the punch tips and takeoff plate. To assist in tablet ejection, several technologies are available, including: • Air-assisted takeoff using a low-pressure air stream, either coming from a dedicated line or using a sin- gle tablet reject line; • Deionizer misters, which eliminate static energy buildup on minitablets that can affect the ejection stream; ters is usually optimal for minitablet production, which is shallower than the depth used for standard tablets. A more precise formula to select the right fill cam depth is: M F = D − C + 2 mm x where F = fill cam depth M = intended tablet weight D = bulk density of your formulation C = cup volume, as shown in your tablet drawing x = cross-sectional area of your tablet, as shown in your tablet drawing Tablet diameter (mm) 1.575 2.5 3.393 Cup depth, deep convex (mm) 0.302 0.48 0.651 Tablet weight (mg) 2.5 10 25 Tablet perimeter (mm) 4.948 7.854 10.659 Tablet thickness (mm) 0.87 1.31 1.69 Tablet volume (mm3) 2.174 8.696 21.740 Land width = 0.05 mm Cup angle (degrees) 44.5 43.6 43.2 Edge XA (mm2) 0.0013 0.0012 0.0012 Edge volume (mm3) 0.0130 0.0192 0.0254 Friability loss, 50% of edge (mm3) 0.0065 0.0096 0.0127 Total friability (% of tablet) 0.30 0.11 0.06 Land width = 0.10 mm Cup angle (degrees) 47.4 45.3 44.4 Edge XA (mm2) 0.0061 0.0054 0.0051 Edge volume (mm3) 0.0605 0.0844 0.1087 Friability loss, 50% of edge (mm3) 0.0302 0.0422 0.0544 Total friability (% of tablet) 1.39 0.49 0.25 Land width = 0.15 mm Cup angle (degrees) 50.7 47.1 45.7 Edge XA (mm2) 0.0177 0.0135 0.0123 Edge volume (mm3) 0.1753 0.2119 0.2631 Friability loss, 50% of edge (mm3) 0.0876 0.1060 0.1315 Total friability (% of tablet) 4.03 1.22 0.61 Table 3 Influence of tablet size and land width on friability and cup angle for minitablets with a deep, convex cup profile