Aqueous Film Coating: Get It Right the First Time

Operational Excellence & Lean Six Sigma Spray gun geometry and calibration Adhesion of particles to the gun surface. This article will concisely present those parameters, review a few of the nuts and bolts of film coating, and offer troubleshooting tips. Some coatings are not suspensions — for example, a clear coating or a controlled-release membrane. However, most coatings are formulated during the suspension process. Typically, a coating formula will consist, roughly, of 7 to 18% film-forming polymer, 0.5 to 2% plasticizer, and between 2.5 and 7% pigment or colorant. Table 1 summarizes the materials typically used. The equipment should mix the suspension thoroughly. Operators must check for even distribution of powders. Lumps and fish eyes should not be allowed, and the suspension should be suspended through an 80-mesh screen. It is important to mix the suspension during preparation, but to stir during actual use. These terms must be written correctly on the batch record, since FDA is very sensitive to their improper usage. The coating equipment and its setup are critical to coating success, and that equipment includes not only what the operator sees, but also what he or she does not see. Pumping systems, coupled with magnetic flow meters, are typically used to deliver coatings. Choices include gear pumps, used for non-suspension coatings, and peristaltic and rotary lobe pumps. Each has its pros and cons, which are summarized in Table 2. Spray gun geometry and calibration Placement of the spray gun (photo, below right) relative to the bed, and boom placement in particular, is very important, yet it is typically overlooked during scaleup or product transfer. The ideal placement will vary between equipment manufacturers and pan models. will generally result in overwetting. will cause solution to stick to the pans. The gun-to-bed distance is fixed, never a range, and the