Coatings

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  • This would appear to be a very good reason for painting anything (film coating is a painting process) and while the penalty for coating tablets the wrong colour is unlikely to be so extreme, the Queen (FDA, MCA, etc.) is likely to extract very costly and damaging retribution. No doubt ‘heads would roll’ metaphorically. So why are tablets coated? After all, it is a messy, complicated and expensive process.

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  • The chapter commences by reviewing the properties of the broad classes of materials used in film coating, polymers, plasticizers, pigments and solvents (or vehicles). An initial consideration of the polymers shows that while processing is most commonly performed using these materials in solution, there are systems which utilize polymers in suspension in water. The mechanism of coalescence and film formation for these types of materials are discussed.

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  • Mechanical properties of film coats Michael E.Aulton SUMMARY This chapter discusses the need for a film coat to possess the correct mechanical properties. One of the requirements of a film coat is that it should provide adequate protection to the dosage form. The capacity of the film coat to afford physical protection depends to a large extent on its mechanical characteristics. After considering those desirable properties, the chapter explains how to assess such properties. It also explains the need for a standardized approach to film preparation prior to testing.

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  • The chapter commences with a brief introduction to the technique of sugar coating, which includes a note on the advantages and disadvantages of this method of coating. The various sequential steps involved in sugar coating are covered in some detail, i.e. sealing, subcoating, smoothing, colour coating, polishing and printing. In the section dealing with subcoating several suitable formulations are provided with details regarding application. Traditionally the colour-coating step in sugar coating has received much attention as the aesthetics of this dosage form are most important.

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  • Solution properties and atomization in film coating Michael E.Aulton and Andrew M.Twitchell SUMMARY A little-considered stage of the film-coating process is the atomization of the coating solution by the spray gun. This chapter will show how formulation and process factors can cause marked changes in the characteristics of the spray, which may have important consequences for film formation and film properties.

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  • The coating process Graham C.Cole SUMMARY In recent years tablet coating has undergone several fundamental changes. The original sugar-coating technique has been largely replaced by film-coating processes using organic solvents. The organic solvents are now being replaced by water because of the development of suitable polymers, improvements in the coating process, and legislation regulating the discharge of pollutants into the environment.

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  • Film coat quality Michael E.Aulton and Andrew M.Twitchell SUMMARY This chapter discusses the desirable properties of polymer film coats with respect to their end usage. The mechanical properties of films were discussed fully in Chapter 12 and so this chapter concentrates on other aspects of film quality such as gloss and roughness, uniformity of film thickness and defects such as cracking, edge splitting, picking, bridging and foam filling of intagliations, etc.

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  • Surface effects in film coating Michael E.Aulton SUMMARY This chapter will explain the significance of the stages of impingement, wetting, spreading and penetration of atomized droplets at the surface of tablet or multiparticulate cores. It will explain some of the fundamental aspects of solid-liquid interfaces which are important to the process of film coating. This chapter will emphasize the importance of controlling the ‘wetting power’ of the spray and the ‘wettability’ of the substrate, and will explain how this can be achieved by changes in formulation and process parameters.

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  • Covers all basic aspects of the chemistry of resins and binders, their solubility in solvents, and their compatibility with pigments essential for modern coating material. Presents state-ofthe-art knowledge of organic coatings materials and their manufacturing and processing. DLC: Gums and resins.

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  • Environmental considerations: treatment of exhaust gases from film-coating processes Graham C.Cole SUMMARY Solvents such as acetone, methylene chloride, chloroform, ethanol and methanol must be prevented from entering the environment. Two options are available: convert all the processes to aqueous-based formulations or recover all the solvent by the use of an appropriate system. Recovery is expensive and is generally the reason for pharmaceutical companies to convert coating formulations to aqueous systems or formulate aqueous coating for all new products.

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  • Automation of coating processes Graham C.Cole SUMMARY Current Good Manufacturing Practice (cGMP) and the demands of the regulatory authorities worldwide requires greater care in the design of manufacturing facilities, the selection of materials used in their construction, their layout, the equipment used in the preparation of tablets to be coated and the coating operation. It is claimed that robotic systems will eventually take over all processing tasks! (Kanig & Rudic, 1986).

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  • Coating pans and coating columns Graham C.Cole SUMMARY This chapter provides some examples of the type of equipment that is currently available. It is not exhaustive, but will highlight the main features that should be considered when evaluating and selecting appropriate units together with ancillary equipment for spraying and control of the coating process. 8.1 CONVENTIONAL COATING PANS It is not proposed to discuss in detail the use of conventional coating pans as these are being phased out with the preference for more sophisticated pans and systems.

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  • Validation of tablet coating processes Graham C.Cole SUMMARY Validation is a concept that means different things to different people. This chapter will highlight all the activities that are necessary to ensure that all aspects of the coating process are fully documented from design through to operation, to provide compliance with regulatory requirements. ‘If it hasn’t been documented, it hasn’t been done.’ FDA 11.

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  • The development of film-coating processes Graham C.Cole SUMMARY To develop a film-coating process requires a laboratory test rig that can be scaled-up to meet production requirements. All the process parameters need to be optimized. A scheme is discussed here that provides an integrated computer-controlled system designed for aqueous film coating in a side-vented pan. A comparison is made of energy requirements of a column-coating system and a coating pan. All the major operational coating parameters can be measured and recorded under the overall control of a microcomputer.

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  • Modified release coatings John E.Hogan SUMMARY Relevant aspects of the composition and performance of modified release coatings are considered in this chapter. Initially, the basic characteristics of multiparticulate systems are described and comparisons are made with the performance of whole tablets intended for modified release. The properties and effects of the polymers and plasticizers which are used in modified release coatings are illustrated with examples from the literature. This further develops the basic treatment of these materials provided in Chapter 2.

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  • This chapter contains a comprehensive listing of research papers, reviews, book chapters and theses covering the subject of pharmaceutical film coating. Coating is a very extensive subject and so this bibliography is restricted to those publications of direct pharmaceutical relevance or authorship. Nonpharmaceutical polymer science or coating processes of other industries are not included. While the listing is extensive, it is by no means exhaustive. Indeed, the author would welcome notification of any missing articles in order that this work can be included in the next edition.

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  • Some common practical questions and suggested answers During the development of coating formulae and processes, common problems tend to recur. This section brings together a collection of typical queries and provides suggested solutions. 1. Question: What major process and formulation parameters do I need to take into account in the change from organic solvent coating to aqueous coating? Answer: Looking first of all at the formulation-based parameters, there is a need to increase the solids loading of the coating suspension to something like 12 %w/w if using a typical HPMC-based formula.

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  • Dieter Stoye, Werner Freitag (Editors) Covers all basic aspects of the chemistry of resins and binders, their solubility in solvents, and their compatibility with pigments essential for modern coating material. Presents state-ofthe-art knowledge of organic coatings materials and their manufacturing and processing. DLC: Gums and resins. This hook was carefully

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  • Thermal noise from optical coatings is a growing area of concern, and overcoming limits to the sensitivity of high-precision measurements by thermal noise is one of the greatest challenges faced by experimental physicists. In this timely book, internationally renowned scientists and engineers examine our current theoretical and experimental understanding. Beginning with the theory of thermal noise in mirrors and substrates, subsequent chapters discuss the technology of depositing coatings and state-of-the-art dielectric coating techniques used in precision measurement.

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