The tablet coating process is widely used in pharmaceutical manufacturing and can also be adapted for nutraceuticals, confectionery products, and other similar products. If your product requires tablet coating, please read this article. A thorough understanding of this process will help you make informed decisions regarding equipment purchases and ensure production efficiency.
What Is the Tablet Coating Process?
The tablet coating process refers to a manufacturing process that uses coating equipment to uniformly apply a layer of coating material to the surface of a tablet. Coating can improve the appearance of tablets, enhance stability, mask bitter tastes, protect active ingredients, and enable special delivery functions such as controlled-release or enteric coating.
Procedure of Tablet Coating Process
The specific procedures for different coating techniques have some differences. But overall, they follow the same basic framework.
- Loading: Place the tablet cores into the coating machine’s drum to prepare for the coating process.
- Tumbling and Preheating: As the equipment operates, the tablet cores are continuously tumbled, while the chip bed is preheated by a hot-air system to reach the temperature required for the process.
- Spray Coating: Using a spray system, the coating solution is evenly sprayed as tiny droplets onto the surface of the rolling tablet core.
- Hot Air Drying: At the same time, introduce heated and dehumidified hot air to enable the solvents in the coating solution to evaporate rapidly.
- Repeated Spraying and Drying: The spray-drying cycle is repeated multiple times until the coating thickness meets your requirements.
Types of Tablet Coating Process
Sugar Coating
The tablet sugar coating process is a traditional process that uses a syrup primarily composed of sucrose to form a thick sugar coating by applying it in layers to the surface of the tablet core. The sugar coating can effectively mask the smell of the tablets and give them a better appearance. If your product lacks palatability, you could consider this process. However, the sugar-coated tablet is significant increase in weight.
Film Coating
Film coating is the process of spraying a polymer-containing coating solution onto the surface of a tablet and drying it to form a film. It is the mainstream technology for modern tablet coating. The thickness of the film coating is usually 20 to 80 micrometers, accounting for 1% to 10% of the initial weight of the tablet core.
Different film coatings have different performances. The conventional film coating focuses on protection and appearance. The moisture-proof film coating can protect APIs that are sensitive to humidity. The sustained-release film coating can achieve the continuous release of the drug.
Enteric Coating
Enteric coating is a type of functional film coating. This coating remains stable and does not dissolve in the acidic environment of gastric juice (typically pH 1–3.5). It dissolves only when the tablet reaches the small intestine, where the pH rises higher, triggering drug release.
The enteric coating must ensure the integrity, because any perforation could cause the drug to be released prematurely in the stomach. Therefore, enteric coatings generally require tighter control of coating uniformity and sufficient film thickness to ensure acid resistance.
Compression Coating (Press Coating)
Compression coating, also known as the tablet-in-tablet technique, is a dry coating method in which the coating material is compressed together with the tablet core. Since no coating solution is applied, compression coating eliminates solvent evaporation and greatly reduces drying requirements compared with conventional film coating. For heat-sensitive drugs and special formulations that cannot tolerate solvents, you can adopt this technology.
Tablet Coating Process Equipment
Standard Coating Pan (Conventional Coating Pan)
Standard coating pans are the most widely used in the pharmaceutical industry. Their basic design consists of a circular metal pan with a diameter ranging from 6 to 80 inches. The pan is inclined at an angle typically ranging from 30° to 45° towards the operating surface. An electric motor drives the pan to rotate about a horizontal axis, causing the tablets in the pan to roll.
The standard coating pan can be supplied with the coating solution by spraying or pouring. To enhance the coating efficiency and uniformity, it is generally recommended to use the spraying system.
Perforated Coating Pan
The perforated coating pan is an improved design of the standard coating pan. The pan body adopts a perforated structure, allowing hot air to pass through the powder bed and then be discharged from the rear of the pot, achieving through-drying.
This design makes the temperature in the spray area more uniform and significantly reduces the risk of over-spraying during drying. The heat exchange efficiency is significantly higher than that of traditional pots.
Fluid Bed Coater (Fluidized Bed Coater)
The working principle of the fluid bed coater is different from that of the coating pan. The tablets or granules are in a suspended fluidized state under the action of the upward blowing airflow, forming a circulating and rolling material bed layer in the chamber. Depending on the design (bottom-spray, top-spray, or tangential-spray), the coating solution is sprayed onto the fluidized particles.
The fluidized bed coater can achieve high coating uniformity and is particularly suitable for coating fine particle-sized materials.
Continuous Coating System
The continuous coating system is an advanced technology that has emerged in recent years. Compared with the traditional batch-based coating process, it has significant advantages. Continuous coating systems offer enhanced process control, reduced batch-to-batch variation, and improved manufacturing efficiency. And the material loss is greatly reduced. It also has a higher degree of automation and less personnel intervention.
Advantages of Tablet Coating Process
Sugar Coating
The appearance is bright and smooth. The thick sugar coat provides mechanical protection and can help isolate unpleasant tastes and odors. If your product is for children, it is a suitable choice.
Film Coating
The film coating hardly increases the size or weight of the tablets, and does not affect the swallowing experience. Film coating generally requires a shorter processing time than sugar coating, but the actual cycle times depend on batch size and coating requirements. What’s more, it has diverse functions and can be designed as a moisture-proof coating, enteric-coated, etc.
Enteric Coating
Enteric coating effectively protects APIs that are unstable in gastric acid and reduces irritation to the gastric mucosa. It also allows the drug to be released at a specific location in the intestine, thereby improving targeted drug delivery.
Compression Coating (Press Coating)
The coating process can be carried out without the use of water or organic solvents, without the need for heating or drying. So it is friendly to heat-sensitive drugs. And it fundamentally avoids the safety risks caused by solvent residues.
Drawbacks of Tablet Coating Process
Sugar Coating
The sugar coating process is very long. The total processing time may reach several hours or even several days. And the sugar coating layer is thick, which significantly increases the weight and size of the tablet. This may affect the swallowing experience. Additionally, your core tablet needs to have sufficient strength to withstand the prolonged rolling during the coating process. Furthermore, if your product requires sustained release, this method is not suitable.
Film Coating
Film Coating requires strict process control. Fluctuations in parameters such as spray rate and inlet temperature can all affect the coating quality. Improper operation may lead to defects such as sticking of tablets, uneven coating, and peeling. Moreover, its ability to mask odors and improve appearance is limited.
Enteric Coating
The process control requirements for enteric coating are high, and any minor defect may lead to serious quality problems. And the material cost of enteric coating is significantly higher than that of conventional film coating. Moreover, the pH values of the gastrointestinal tracts of different patients vary, which will affect the actual release of the enteric-coated materials.
Compression Coating (Press Coating)
Compression coating has high technical requirements. It requires specially designed tablet molds and pressing equipment. Moreover, the formulation development and process validation are more complex than those of the traditional wet process, so the research and development cycle is longer.
Applications of Tablet Coating Process
Tablet Coating Process in Pharmaceutical Industry
In the pharmaceutical industry, coating is used to mask bitter tastes, protect active ingredients sensitive to stomach acid, and achieve functions such as enteric, sustained-release, and controlled-release formulations. It also improves the palatability of pediatric medications and the moisture resistance of traditional Chinese medicine tablets.
Healthcare Product
In the nutritional and health supplement sector, coating can mask the unpleasant odors of ingredients such as fish oil and garlic oil, enhance product stability, and improve the swallowing experience. The moisture-proof coating can also extend the shelf life of the product.
Food Industry
In the food and confectionery industries, similar coating technologies are also used in confectionery manufacturing to improve gloss, appearance, and texture. If you want to make your products more appealing and improve their market competitiveness, coating is a common and effective solution.
Veterinary Medicine and Agriculture
In veterinary drug formulations, coating aids in masking flavors and providing stability protection. Additionally, similar coating principles are used in agriculture to produce controlled-release fertilizers and to extend the nutrient release cycle.
FAQ
What Is CIP? What Significance Does It Have for the Tablet Coating Process?
CIP is a system that can automatically clean the interior of production equipment without disassembling it. Since coating film-forming substances tend to adhere to the spray gun arms of the coating machine and other inaccessible surfaces, manual cleaning is difficult. The CIP system removes residues through automated processes such as pre-washing, detergent cleaning, and rinsing. Packages equipped with CIP can not only significantly shorten the cleaning time but also meet the cGMP requirements for preventing cross-contamination.
What Are the Differences between Using Organic Solvents for Coating and Water-Soluble Coating in the Tablet Coating Process?
Organic solvent coating has a faster drying speed and is more suitable for APIs that are sensitive to moisture. But it is necessary to strictly comply with residual solvent regulations.
Water-based coating uses water as the solvent and has higher safety and environmental performance. However, water-based coating requires stricter process control, and the temperature of the tablet bed needs to be more precisely controlled. You can make the choice based on the water sensitivity of the API and the factory’s safety production management capabilities.
How to choose Tablet Coating Process Equipment?
When choosing tablet coating equipment, consider production scale, coating type, and your budget. For small-scale production or sugar coating, we recommend standard coating pans. For large-scale film coating and aqueous coating, perforated coating pans are suitable. For microtablets or controlled-release coating, fluid bed coaters are the top choice. If you pursue production efficiency, low batch difference, and have enough budget, a continuous coating system is a good choice.
How Can Orange Peel Defects Be Avoided in the Tablet Coating Process?
Orange peel occurs when coating droplets begin to dry before they can spread evenly across the tablet surface. Common causes include excessive atomization pressure producing overly fine droplets, high coating solution viscosity, high inlet air temperature, or insufficient spray rate.
To prevent orange peel, optimize atomization pressure, maintain appropriate coating viscosity, and balance spray and drying conditions to allow the droplets to spread properly before film formation.
What Are the Effects of Excessive Inlet Humidity in the Tablet Coating Process?
Excessive humidity will slow down the drying process and may cause tablets to stick together or the coating to turn white. During the tablet coating process, the dew point of the incoming air must be controlled. The relative humidity typically should be kept below 45%, but the actual situation depends on the formulation and process design. You can use dehumidifiers if necessary.
Final Thoughts
If you want to order tablet coating machines or have any related questions, please feel free to contact us. Pilotech is a professional manufacturer of tablet coating machines. No matter what industry you are in, pharmaceuticals, food, or chemicals, we will provide you with customized solutions.