Glatt. Coater

TABLET COATING

Tablet coating is the process of evenly covering particles with a substance by applying a series of thin layers. These coaters differ in their function and application.

(Copyright Rob Main)

HORIZONTAL PAN

Layers of coating spray are applied to the particles until a desired thickness is achieved. For example, a coating of glaze gives candy its glossy sheen.

(Copyright Nicos Group, Inc., Norwood, NJ)

GENERAL INFORMATION

Tablets are loaded into the machine at the beginning of each batch. They tumble on a rotating drum while a coating liquid (solution, dispersion, or melt) sprays through nozzles onto their surface. Meanwhile, fans direct heated air through the tablets and the perforated drum, as shown below. This air either evaporates the solvent or cools the melt. Below are diagrams for fully perforated, to the left, and integrated plenum rotating pans, to the right. The integrated plenum pans operate effectively at lower airflows, which make them better suited for solvent coating applications.

(Copyright Vector Corporation, Marion, IA)

This process continues until the tablets are sufficiently coated, at which point they are discharged from the machine.

EQUIPMENT DESIGN

Four systems make up a pan coater: the drum, the spray system, the charging mechanism, and the control system.

The Drum

The three key elements of a drum are its size, perforations, and baffles.

Research-size drums hold about 10 liters of material while industrial-scale drums can hold more than 2, 000 liters, or about 2 tons of material. Some pan-coating machines will accept various drum sizes.

The size of the perforations restricts the size of tablets the drum is capable of processing. As the drum rotates, the baffles churn the tablets to prevent sticking and to ensure that they all receive an equal coating.

(Copyright Vector Corporation, Marion, IA)

The Spray System

The core of the pan-coater, and most other coating machines, is the spray system. The more effectively the spray system atomizes the coating suspension, the more evenly the tablets get coated. Batch-to-batch consistency is a consideration in the pharmaceutical industry. Shown below are examples of spray systems.

(Copyright Vector Corporation, Marion, IA)

To achieve this optimal spraying, the nozzle is selected to suit the type of suspension being applied. Sugar coating machines conventionally use a rake, while aqueous and organic suspensions use binary nozzles.

Charging and Discharging Systems

To charge the pan, tablets are typically poured down a chute that empties into the drum. However, some applications require closed charging. In these cases, the tablets enter the machine through a pipe in the front or on top of the pan.

(Copyright Nicos Group, Inc., Norwood, NJ)

Control Systems

The machine must be monitored to ensure batch-to-batch consistency and quality. Modern coaters use computer software, such as the program pictured below, to achieve this. The computer can monitor a number of parameters, such as: the temperature of the incoming air, the humidity, the drum spin-rate, and the spray-rate.

(Copyright Nicos Group, Inc., Norwood, NJ)	(Copyright Rob Main)