Scale film coating process

Unlike the processes described elsewhere in this book, the film-coating process is inherently much more complex, since the list of parameters that contribute to overall success is, potentially, exhaustive. Thus, the complexities of the scale-up process are potentially more challenging. In basic terms, these three components of the film-coating process all contribute, in a very much interactive manner, to the overall success of the process ... 

Considering the processing fundamentals of this dry process, almost all of the issues associated with the scale-up of more traditional film-coating processes are eliminated, and the key objective is to feed tablets directly from the tablet press into the electrostatic coating operation, and thence in to packaging. Thus, once the process is defined in terms of coating one tablet, it is replicated an appropriate number of times in order to coat all of the tablets in the batch. 

Table 7 Example of Operating Parameter Ranges Used When Scaling Up an Aqueous Film-Coating Process...

To date, use of such continuous processes has been restricted primarily to the manufacture of large-volume products, an application for which continuous processes potentially have a major advantage. Nonetheless, continuous coating processes provide a potentially viable alternative for the scale-up of any film-coating process, where many of the tasks potentially become much simpler, since they would always be the same irrespective of whether the production batch size is 250 kg or 5(K)() kg. Simplification arises from reducing or eliminating tasks that would... 

Scale-up of a film-coating process is dependent on the functionality of coating. A non-functional coating used to mask color change and taste, or used for identification, is considered a non-critical step, and optimization is made to maximize coating time. The assumption is made that standard coating formulations are used... 

As with ah thin-film PV technologies, the projected manufacturing costs of a-Si H ahoy PV modules fah rapidly with annual manufacturing volume, ie, MWp /yr. The primary driver of this volume cost reduction is the volume—cost relationship of commercially available thin-film processing equipment. Thin-film coating machines often have capacities equivalent to 3—5 yr, so that manufacturing economies of scale are more fully realized at the... 

Since the majority of film-coating operations around the world utilize aqueous coating processes, it is often useful to apply thermodynamic models to the process. In this way, the development-scale process can be fundamentally characterized, based on application of the first law of thermodynamics, as suggested by Ebey (6), allowing more accurate predictions for operating... 

The potential benefits of CVD over other film deposition techniques are that CVD-derived films can be deposited under conditions that give conformal coverage, they can be deposited at low temperatures, there can be a high level of compositional control, thin layers can be deposited, the technique can be scaled to coat large areas uniformly, and there is also the possibility for area-selective deposition13 as a result of the chemical nature of this process. The details of CVD and related chemical deposition processes such as atomic layer epitaxy (ALE), organometallic vapor-phase epitaxy (OMVPE), and others have been described elsewhere.6... 

The second approach to coating scale-up involves an understanding of thermodynamic and mass transfer processes. A robust process can be demonstrated by establishing a coating procedure that identifies critical process parameters and their effect on the equilibrium between mass flow (the coating solids applied) and heat transfer (the solvent removed). This approach allows one to evaluate air temperature, air flow, and spray rate as applied to a known mass of tablets, and then scale these conditions into a larger coater. A thermodynamic model for aqueous film coating as described by Ebey is shown in Eq. (9). 

When diffusional relaxation of a suspension brought out of equilibrium by shearing is slow with respect to the time-scale of the process (De number), the suspension is said to be thixotropic. This behaviour is illustrated in Fig. 6.21. Thixotropy is usually imwanted in ceramic membrane support coatings, but does occur for some suspension formulations. The layer thickness obtained in film-coating with the same suspension but with a different shear history can then differ. 

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