Laboratory Coater ensures homogeneous and reproducible results - Publication from Pharma + Food

Tablets should be evenly coated with the respective film during coating. A new Laboratory Coater enables companies to achieve a homogeneous coating with batch sizes between 0.15 and 13 litres.

Decision-maker facts

• The entire air technology as well as the electrical and control technology is integrated into the lab coater.
• The system can be operated with three different drum sizes.
• Anti-bearding caps (ABC) prevent product build-up.

Tablets are the most important oral dosage form in the pharmaceutical industry and are therefore produced in large quantities. In addition to efficacy and functionality, the size, colour and shape of the tablet influence the marketing of the preparation.

In Tablet Coating, a thin film is applied to the tablet, which consists of one or more polymers and other functional excipients such as colourants or humectants and can fulfil various functions. Tablets are coated to modify the release of the Active Pharmaceutical Ingredient (API), to protect the API from light or moisture or to mask a bitter taste in the tablet formulation. Tablets are also coated to improve swallowability.

When developing preparations or improving products, users usually start by using an existing formulation. The basis for each coating is often a previous formulation that is modified, for example to make the coating harder or to improve binding to the core of the tablet.

Up to four different film types

Active Pharmaceutical Ingredient (API) coating is becoming increasingly important, with both combination preparations and the combination of two incompatible APIs in one dosage form being realised. In addition, different release profiles of the same Active Pharmaceutical Ingredient (API) can also be combined. The core contains the slow-release component and the tablet coating contains the fast-release initial dose.

The formulation approaches sometimes consist of up to four different film types. This leads to long process times. In order to successfully develop and produce such formulations, it is essential that the tablets are uniformly coated, the so-called coating uniformity.

Flat tablet bed reduces the melt pressure

The interaction between mixing, spraying and drying is crucial in Tablet Coating. These process steps must be carried out simultaneously and with the correct settings in order to achieve a uniform coating.

The tablet cores must be moved evenly and gently under the spray cones, as they will be damaged if subjected to excessive mechanical stress. L.B. Bohle has been using an extended coating drum (length diameter (L/D) > 1) with welded-in mixing spirals for more than 20 years. The mixing spirals mix the tablet bed continuously and gently. Homogeneous mixing is achieved after just a few minutes and is maintained over the entire process time. The flat tablet bed reduces the melt pressure in it.

Tablet breakage and twin formation do not occur, as the continuous guidance of the mixing spirals does not accelerate the tablets significantly.

Up to 40 % shorter process times

The drum geometry of the manufacturer's BFC Tablet Coater creates a large spraying surface in the moving tablet bed, which means that more spray nozzles can be used than with shorter drums. This results in a larger spray area and a higher spray throughput. In addition to the coating suspension, the nozzle type, number and spacing are of particular importance.

As a rule, the proportion of suspension mass in film-coated tablets is 5 to 15 % in relation to the mass of the core. Special mention should be made of the film thickness, which is not only important for active ingredient coatings, but must also be uniform for thin colour (protective) coatings. An uneven film application within a batch, for example, leads to colour differences that reduce product quality. Compared to conventional Tablet Coaters with L/D ratios <1, systems with extended drums enable up to 40% shorter process times due to higher spray rates.

The decisive factor is that optimum energy and mass transfer is possible. This means that the energy must be introduced directly into the tablet bed. The air flows directly and calmly into the tablet bed and ensures that the sprayed suspension dries quickly. The periphery of the coater and the housing are not heated. The spray nozzles are not exposed to the supply air flow and remain cool during the spraying process. This minimises spray drying effects and achieves a coating uniformity of > 97 % and better.

Mini drum for test or very small batches

The manufacturer has designed the new BFC 5 Laboratory Coater for batch sizes of up to 13 litres on the basis of an existing system. In addition, the manufacturer has defined requirements that the new generation of machines should fulfil through close dialogue with users and market analyses.

The Laboratory Coater is a flexible, mobile stand-alone machine in which the entire air technology as well as the electrical and control technology are integrated. It is operated via a multi-panel visualisation with touch panel. The rotating operating unit is located directly on the coater. Commissioning is quick and uncomplicated; all that is required is an electrical connection and a compressed air supply.

The Laboratory Coater can be operated with a total of three different drum sizes - with the same drum geometry. The system is equipped with two drums as standard. This allows batch sizes (volume up to the edge in litres) of 2 to 6 l or 5 to 13 l to be realised. The smaller drum enables batches of 0.5 to 3 litres by using a separating disc. A transport trolley is included as standard for easy removal and transport of the drum. Users can then save all the results achieved and scale them up to larger batches.

A new slotted mini drum for test or very small batches of 150 to 350 g now offers even more flexibility. The manufacturer has equipped the slotted drum with a corresponding perforation in which users can film not only normal-sized cores but also cores with a diameter of 1.5 mm. The small drum is therefore an effective and profitable addition, especially in product development and for cost-intensive Active Pharmaceutical Ingredients (API) or formulations.

Nozzle arm with mini pump head

The nozzle arm is modular: Depending on the application, one to four nano-nozzles from the Schlick company are inserted. Other Laboratory Coaters on the market sometimes only have one spray nozzle. A hose pump head, into which all four hoses fit, supplies each nozzle individually. This leads to a homogeneous and reproducible spraying result. The anti-bearding caps (ABC) prevent product build-up.

In the new system, the process chamber and sensors are more easily accessible thanks to a larger door and two integrated lights give the operator an overview of the machine's status at all times. The manufacturer has also improved the cleaning of the Laboratory Coater: three cleaning nozzles ensure complete wetting and cleaning of the entire surface. A new fill level sensor ensures that there is no overfilling. Instead of the previously manually adjustable pressure control for forming and atomising air, this is now integrated into the machine via the software as standard; this makes the process more accurate by minimising deviations.

Link to the original article: Pharma + Food