Tablet Coating Tablet coating is the process of evenly covering particles with a substance by applying a series of thin layers. The film coating involves coating the tablet core with thin film of polymer, The film coating process is highly favored because the weight increases to 2-3%, only takes a single stage process, can be controlled with ease, easily retains the color of the original core, automation is possible and adaptability to GMP, Film coating makes use of Accela cota and fluidized bed equipment. The enteric polymer has the ability to form a direct film during the film coating process. The core of the tablet is usually weak and has high propensity for disintegration. Evaporation of the water from the sprayed film is driven by the heated pan whereas organic vapors are removed via the vacuum system. The polymer that is to serve as the coating film is dissolved in a suitable solvent, together with additives such as pigments and plasticizers. Tablet film coating is a technology-driven process and the evolution of coated dosage forms relies on advancements in coating technology, equipment, analytical techniques, and coating materials. Once the core is dry, a sealing coat is applied to protect the core from absorbing any moisture. Pharmaceutical tablet coating involves the application of a coating composition to a moving bed of tablets with the use of heated air to facilitate the evaporation of the solvent. Definition: Cratering happens when a defect on the film’s coating results in craters appearing on the tablet which in turn results in the exposure of the tablet’s surface. The materials in the coating process contain ionic species that are of opposite charge which are then sprayed onto the charged substrate. To distribute a suspended colourant equally, the coating solution requires the use of powdered colourants. Disadvantages – When used by itself HPMC is inclined to bridge or fill up the debossed tablet’s surface. Tablet coating is a very important aspect of the manufacture of commercial tablets. Viscosity levels range from medium, high and extra high. The solution usually contains a mixture of starch, pigments, acacia, gelatine, and opacifier if needed. This is not used as often as the HPMC because it is soluble in only few organic solvents. FILM COATING:- As the sugar coating process is very time consuming and is dependent on the skills of the coating operator, this technique has been replaced by film coating technology. In formulating a new film it is useful as a first step to be able to cast a trial film by spreading the coating solution onto a flat surface of Teflon, aluminum foil or glass using a spreading bar to achieve the preferred thickness. Once these materials are mixed and homogenised the solution is then sprayed on the tablets. The most commonly used lakes and dyes are the certified FD, C and D/C colourants. © 2020 LFA Machines Oxford LTD. All Rights Reserved. Grossing (Smoothing) – this is often carried out in stages. Latest techniques make use of spray system and automation to increase coating efficiency and uniformity of the end product. Organic rather than aqueous solvents are effective and ideal for the vacuum film coating system as there are minimal safety and environmental concerns. The D Series features a double wall construction which leads to better thermal efficiency, better sound absorption and ease of cleaning. Four processes are commonly employed in sugar coating, in the following order: Sealing (Water proofing) – sealing involves hardening the external surface of the tablet by providing a moisture barrier. The coating requires a specialized tablet press machine. Although specialized equipment has been developed for dip coating, no commercial application for it has been attained. Other advantages include delaying the enteric properties and preventing the separation of the incompatible ingredients. The sealing coat is altered by adding one of the enteric polymers in sufficient number in order for it to pass the enteric test for dissolution. For sugar or film coating, lakes are preferred because they produce more reproducible results. Finally the tablets are dried, which remove the excess solvent leaving behind a thin coating of the solvent around the core of the tablet. Lakes are preferred as they show viable results. Tablet coating is used to improve the tablet’s appearance and has the added benefit of providing pharmaceutical companies a surface on which to imprint information or branding. This is due to the rough tablet to tablet impact as well as the tablet chamber contact. Causes : Cratering can occur in certain instances where there is insufficient drying time to seal the film or a high volume of coating solution is applied. There are 2 kinds of layering - 1 layer and 2 layer system. Equipment Efficiency – coating efficiency is achieved by dividing the net increase in the weight by the total of the nonvolatile coating applied to the tablet. The sugar coating is generally water-soluble making it easier to dissolve quickly when it comes into contact with any liquid medium such as gastrointestinal fluids. The ideal coating should be at 90-95%. The base formula for every coating is usually achieved taking a previous formula and modifying it to improve the bond of the coating with the core of the tablet, increasing the hardness of the coating etc. The following should be noted: In addition, the following may be required: 1-Layer System – the formulation is coated in one contiguous layer either in colour or as a white-opaque layer. The higher molecular weight PEG appears as an off-white wax at room temperature. Partially dried films are considered tacky and as such other additives are used to modify the composition. 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