# Tablet Coating Techniques > Tablet coating techniques in Pharmacy: sugar coating stages, film coating polymers, enteric pH triggers, equipment and coating defects. - Canonical URL: https://prepelephant.com/topics/allied/pharmacy/tablet-coating-techniques - Exam / course: Allied Health · Subject: Pharmacy - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Tablet Coating Techniques", PrepElephant, https://prepelephant.com/topics/allied/pharmacy/tablet-coating-techniques ## Direct answer Coating applies a thin, functional layer to a tablet core for taste masking, moisture protection, elegance or site-specific release, by three broad routes: sugar coating, film coating and press coating. Sugar coating builds a shell of sucrose layers through sealing, subcoating, syrup smoothing, colouring, polishing and printing, and can raise tablet weight by 30 to 50 per cent; film coating deposits a 2 to 5 per cent polymer layer — usually hypromellose in an aqueous dispersion — in a perforated pan or fluidised bed. Enteric coating swaps the soluble hypromellose for pH-triggered polymers such as cellulose acetate phthalate or methacrylate copolymers (Eudragit L and S) that resist gastric acid and dissolve at intestinal pH, protecting acid-labile drugs or the stomach itself. Each process is then judged by the defects it produces — a diagnostic list every practical examiner loves. ## What you must remember - **Sugar stages in order:** seal coat (shellac), subcoat (syrup plus talc to build edges), smoothing syrup, colour coat, polishing with carnauba or beeswax, printing. - **Film coating:** hypromellose (HPMC) is the workhorse polymer, with plasticisers (polyethylene glycol) and pigments at typically 5 to 15 per cent solids; ethylcellulose serves for moisture barriers. - **Enteric triggers:** cellulose acetate phthalate and Eudragit L 30 D-55 dissolve above about pH 5.5 (duodenal release), Eudragit L above pH 6, Eudragit S above pH 7 (colonic targeting). - **Equipment:** conventional pans for sugar work; perforated pans (Accela-Cota type) with heated airflow for film coating; fluidised bed (Wurster) columns for pellets and multiparticulates. - **Process balance:** inlet temperature typically 40 to 50 °C for aqueous film coating; spray rate and pan speed tuned so drying keeps pace with application — wet surfaces pick, hot surfaces spray-dry. - **Defect dictionary:** orange peel (poor spreading), picking and sticking (over-wetting), bridging of monograms (weak viscoelastic film), mottling (uneven pigment), cracking and twinning. - **Speciality coats:** sustained release by ethylcellulose or Eudragit RL/RS membranes; press coating for separating incompatible drugs into core and shell. ## Walking a batch through a perforated pan Seal a batch of bitter cores first with thin shellac to survive the aqueous sprays. Warm to about 40 °C, start the hypromellose dispersion slowly; if the bed climbs past roughly 45 °C the droplets dry in flight and orange peel appears, while too cold leaves tablets tacky and stuck in pairs. The film grows to about 3 per cent of core weight in an hour or two — the elegance of film coating is that a 60 mg layer does the work of a sugar shell ten times heavier. For an acid-labile proton-pump inhibitor the operator switches to a methacrylate dispersion with ample plasticiser, because enteric films are brittle and crack on tablet edges if coalescence is rushed; tablets are then held warm to complete film curing. Final checks are appearance, weight gain, and dissolution — almost no release in acid for two hours, prompt release in pH 6.8 buffer. The coating earns its place only in the dissolution bath. ## How examiners frame coating questions Two inversions dominate. First, sugar versus film coating: candidates recite stages but forget the quantitative discriminator — 30 to 50 per cent weight gain for sugar against 2 to 5 per cent for film, which halves bulk and packing cost, the real reason the industry abandoned sugar. Second, "enteric coat is for taste masking" is a standing error; taste masking needs only a fast-dissolving barrier, whereas enteric coating is defined by acid resistance followed by intestinal dissolution, verified in the disintegration apparatus, not on the tongue. A practical favourite matches defect to cause on a photograph: orange peel with insufficient spreading, picking with over-wetting, bridging with a weak film. Naming the process variable that fixes each — solvent, spray rate, plasticiser, bed temperature — separates a pharmacist from a memorised list. ## Frequently asked questions ### List the stages of sugar coating in order. Seal coating, subcoating, smoothing (syrup) coating, colouring, polishing and printing — each stage fixes the faults the previous stage could not. ### Why has film coating largely replaced sugar coating? A 2 to 5 per cent weight gain masks taste and protects the core as effectively as a 30 to 50 per cent sugar shell, while cutting process time and avoiding the sugar load. ### At what pH do the main enteric polymers dissolve? Cellulose acetate phthalate and Eudragit L 30 D-55 above about pH 5.5, Eudragit L above pH 6, Eudragit S above pH 7 — the polymer is chosen by the release site required. ### What causes orange peel and picking during film coating? Orange peel arises when droplets dry before spreading (insufficient solvent, hot bed); picking when tablets stick and film tears (over-wetting, slow drying) — opposite faults of one drying balance. ### Which equipment coats pellets and multiparticulates? Fluidised bed coaters with a Wurster insert spray particles riding an air column, giving uniform coats to spheres that a rotating pan would agglomerate.