Tablet coating is a critical finishing operation in pharmaceutical solid dosage manufacturing. A well-executed coating process improves patient compliance, protects the API from environmental degradation, masks unpleasant taste or odour, and enables controlled or delayed drug release. Poorly executed coating, however, leads to defects like picking, twinning, logo bridging, and coating non-uniformity — all of which result in batch rejections and regulatory failures.
This comprehensive guide covers the types of tablet coating, the coating process steps, key equipment — especially the Coating Pan — process parameters, common coating defects and their remedies, and GMP best practices for pharmaceutical tablet coating.
We are a leading manufacturer, supplier, and exporter of Coating Pans and the complete granulation and solid dosage equipment range to pharmaceutical manufacturers worldwide.
Tablet coating is the application of a thin film or layer of coating material onto the surface of compressed tablets. The coating material — dissolved or suspended in a solvent or aqueous medium — is sprayed onto tumbling tablets inside a rotating coating pan. The solvent evaporates under a controlled stream of heated air, leaving a uniform coating film on each tablet surface.
Tablet coating serves multiple pharmaceutical functions depending on the type of coating applied. From simple sugar coats for taste masking to sophisticated enteric coatings that survive the stomach and release the drug in the intestine, coating technology plays a decisive role in the clinical performance of the final dosage form.
Film coating is the most widely used tablet coating method in the modern pharmaceutical industry. A thin polymer film — typically 20 to 100 micrometres thick — is applied to the tablet surface using a spray system inside a perforated coating pan. Common film-forming polymers include Hydroxypropyl Methylcellulose (HPMC), Hydroxypropyl Cellulose (HPC), and Polyvinyl Alcohol (PVA). Film coating is classified into aqueous film coating (uses water as solvent; preferred for safety) and organic solvent film coating (used for moisture-sensitive APIs).
Sugar coating is one of the oldest tablet coating methods, producing a smooth, glossy, often coloured finish by applying multiple layers of sucrose-based coating solution. Sugar-coated tablets have a characteristic rounded appearance with a significantly increased tablet weight (typically 30–50% weight gain). While sugar coating is being replaced by film coating in most modern facilities, it remains relevant for traditional formulations and certain herbal products.
Enteric coating applies a pH-sensitive polymer layer that resists dissolution in the acidic environment of the stomach (pH < 2) but dissolves rapidly in the alkaline environment of the small intestine (pH > 5.5). This protects acid-labile APIs such as proton pump inhibitors (PPIs), certain enzymes, and probiotics from gastric acid degradation. Common enteric coating polymers include Cellulose Acetate Phthalate (CAP), Hydroxypropyl Methylcellulose Phthalate (HPMCP), and Eudragit L series polymers.
Modified-release coatings use semi-permeable or water-insoluble polymer membranes to control the rate and location of drug release. Extended-release coatings allow once-daily or twice-daily dosing by slowing drug diffusion through the membrane. Pulsatile-release coatings deliver the drug in timed bursts. These coatings are increasingly important for chronotherapy applications and improving patient adherence.
The Coating Pan is the primary equipment used for tablet coating in pharmaceutical manufacturing. It consists of a rotating stainless steel drum (the pan) mounted on a tilted axis, a spray system for coating solution application, and an air handling unit (AHU) that supplies heated inlet air and extracts humid exhaust air.
| Coating Pan Type | Description | Best Application |
|---|---|---|
| Standard (conventional) Coating Pan | Open pan with side-mounted spray gun; relies on natural air circulation | Sugar coating, traditional formulations |
| Perforated Coating Pan | Pan has perforations for forced air flow through tablet bed; faster drying | Film coating, enteric coating, aqueous coating |
| Side-vented Coating Pan | Side-mounted exhaust ports with baffles; improved air flow uniformity | High-volume film coating |
| Lab / R&D Coating Pan | Small-scale pan (1–5 kg) for formulation development | R&D, pilot batch coating |
Key Components of a Pharmaceutical Coating Pan
| Step | Stage | Details |
|---|---|---|
| 1 | Tablet core inspection | Check tablet hardness, friability, disintegration, and moisture content before coating |
| 2 | Coating solution preparation | Dissolve/disperse polymer, plasticiser, pigment, and other excipients in solvent/water |
| 3 | Pan loading | Load tablets into coating pan at 60–70% pan capacity |
| 4 | Pre-warming | Warm tablet bed to target inlet temperature (typically 50–65°C) before spraying begins |
| 5 | Coating spray | Spray coating solution onto tumbling tablets at validated spray rate and atomisation air pressure |
| 6 | Drying | Maintain inlet air temperature and volume for solvent/water evaporation |
| 7 | Weight gain monitoring | Sample tablets periodically to check coating weight gain against target (typically 2–5% for film coat) |
| 8 | Cooling | Cool tablet bed to below 30°C before discharge to prevent sticking |
| 9 | Discharge | Discharge coated tablets into IPC Bin for transfer to packaging |
| Process Parameter | Typical Range | Impact if Out of Range |
|---|---|---|
| Inlet air temperature | 50–65°C (aqueous) | Low temp: picking/sticking; High temp: over-drying, logo bridging |
| Exhaust air temperature | 35–45°C | Indicator of drying efficiency; low = under-drying |
| Pan speed | 8–15 RPM | Too slow: uneven coating; Too fast: tablet attrition |
| Spray rate | 10–50 g/min (batch-dependent) | Too high: sticking/picking; Too low: slow process, over-drying |
| Atomisation air pressure | 1.5–3.0 bar | Too low: droplet coalescence; Too high: spray drying |
| Inlet air volume (CFM) | Process-specific | Insufficient: under-drying; Excessive: premature drying |
| Coating solution concentration | 10–15% w/w (film coat) | Affects spray rate, droplet size, and film uniformity |
| Coating weight gain | 2–5% (film); 30–50% (sugar) | Below target: inadequate protection; above target: dissolution impact |
| Defect | Likely Cause | Remedy |
|---|---|---|
| Picking / Sticking | Spray rate too high; inlet temp too low | Reduce spray rate; increase inlet air temperature |
| Twinning | Tablets adhering to each other | Increase pan speed; reduce spray rate |
| Logo bridging | Excess coating in embossed logo area | Reduce coating viscosity; increase atomisation pressure |
| Orange peel surface | Spray dried droplets; atomisation pressure too low | Increase atomisation air pressure; reduce spray rate |
| Colour variation | Uneven spray or poor tablet tumbling | Check baffles; optimise pan speed; validate spray pattern |
| Film cracking / peeling | Insufficient plasticiser; brittle film | Increase plasticiser level in coating formulation |
| Weight gain non-uniformity | Uneven spray; poor tumbling | Check spray gun alignment; inspect baffles; adjust pan loading |
| Tablet core erosion | Pan speed too high; friable cores | Reduce pan speed; increase tablet hardness before coating |
The Coating Pan operates downstream of the tablet compression process. Tablets are produced from granules manufactured through the Rapid Mixer Granulator and dried in the Fluid Bed Dryer. After milling through the Multi Mill and sieving via the Vibro Sifter, granules are blended and compressed. The compressed tablet cores are then loaded into the Coating Pan for film or enteric coating. After coating, tablets are discharged into an IPC Bin for transfer to the packaging line.
Tablet coating is a scientifically complex process that demands precise control over equipment, process parameters, and coating formulation. The Coating Pan — supported by a validated AHU, calibrated spray system, and robust process controls — is the cornerstone of a successful tablet coating operation.
A complete solid dosage manufacturing line from our range includes the Rapid Mixer Granulator, Fluid Bed Dryer, Multi Mill, Vibro Sifter, Blenders, and the Coating Pan — all manufactured to GMP standards and available for export worldwide.
Speak with our technical team for expert guidance on coating equipment selection, specifications, and pricing.
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