The ConsiGma™ coater is a revolutionary, new, high performance tablet coating technology that accurately deposits controlled amounts of coating materials on tablets.
Coating Tablets with a Cascade
GEA is an established supplier of traditional coater systems for particles, powders, granules, crystals, pellets and tablets and is able to provide equipment for all the typically used coating technologies and assist with the selection of the process that best suits your needs. Coating is an important unit operation that’s used extensively in the pharmaceutical industry for the application of non-functional or functional coats (aesthetic, protective or rate controlling polymer films) and for the deposition of active pharmaceutical ingredients (APIs) onto nonpareils (multi-particulate dosage forms). Applications include taste masking, color modification, physical protection and/or to create modified release forms.
Beyond efficient API layering techniques for multi-particulate systems, the pharmaceutical industry has an inherent need to accurately coat objects that are 3–30 mm in length (the most common size range for single-unit solid dosage forms) with APIs. These include tablets for oral administration and other delivery methods (human implantation, for example). Existing coating methods in this size range have coating speed and accuracy/uniformity limitations, particularly for the deposition of low dose APIs onto single unit tablet dosage forms. Furthermore, the actual machinery used to coat tablets in the pharmaceutical industry has remained fundamentally unchanged for the past 50 years. That is, until now.
The ConsiGma™ coater from GEA is a revolutionary, new, high performance tablet coating technology that accurately deposits controlled amounts of coating materials on tablets — even if they are hygroscopic or friable. Designed specifically to be an integral part of the ConsiGma™ continuous high shear granulation and drying system, the coater is able to coat small quantities of tablets at very high rates, offering improved heat and mass transfer and using much less coating material than traditional technologies.
Presenting a paradigm shift in tablet coating, this new type of coater subjects tablets to a cascading tablet movement that enables greater fluid application rates (higher coating build-rates) than traditional coating pans. The functionality of enteric coatings, for example, is greatly dependent on weight gain and coating uniformity. In traditional coating pans, fast coating application rates often result in poor uniformity, requiring a higher weight gain to achieve enteric protection. Inconsistent and imperfect, this “standard” practice of tablet coating often delivers a non-homogenous product. Because the tablets are loaded in large rotating pans and vented for hot air drying, tablet edges can get grounded off, intagliations can get filled in by coating material, and edges and corners may not be coated with the same thickness as the tablet faces.
The inaccuracy of coating material deposition limits the use of modified release coatings. In a laboratory setting, it is necessary to coat several kilograms of tablets at one time, making the research and development (R&D) of a solid dosage form costly and difficult. In addition, extremely hygroscopic tablets cannot be coated using current technology, nor can flat or oddly shaped cores be consistently coated. The ConsiGma™ coater from GEA is your solution to these problems.
Based on the small batch capabilities of the SUPERCELL™ Coating Technology (SCT), the ConsiGma™ coater from GEA effectively solves all of these problems. Incorporating a small, simple and modular design, specifically intended for early stage, laboratory scale production, a 1.5–3.0 kg batch of tablets is, under the influence of radial air knives, induced using a centrifugal process to form a stable, gravity free cascade inside a perforated drum rotating at high speed. Increased drying efficiency is achieved by spraying the coating suspension into a cascading cloud of tablets.
The ConsiGma™ coater process is dependent upon the machine’s ability to form a ring of tablets that adhere to the perforated inner surface of the wheel, induce these tablets to form a cascade under the influence of radial air knives and maintain this cascade throughout the coating process. For most tablets this is simply achieved; the speeds, acceleration criteria, knife pressures and times can be preset. Once initiated, there is no need for any further in-process modulation. The process is shown in Figure 1 and described below.
- Filling: The empty wheel is charged with tablets through a trapdoor (Figure 1a).
- Ring Formation: Tablets are formed into a ring by rapidly accelerating the wheel to high speed (Figure 2a).
- Ring Distribution: The ring is distributed by slowly decelerating the wheel to the coating speed under moderate air knife pressure.
- Cascade Formation (and Preheat): Increasing the air knife pressure forms a tablet cascade; the tablets dedust, deburr and preheat (Figure 1c).
- Coating (and Drying): During full, “in flight” cascade, a coating suspension is sprayed onto the cascading tablets, which dry under the influence of heated process air; the spray rate may be varied during the coating process to increase speed or enhance the final appearance; at the end of spraying, a short delay dries off any residual solvent (Figure 1d). Having established the cascade, the coating process is started and runs to completion without loss of cascade or any apparent need for speed adjustment.
- Discharge: Reducing the air knife pressure reforms a ring; the ring is collapsed by decelerating the wheel to a standstill and the tablets are discharged via the trapdoor.
Figure 1: Stages of tablet motion in the ConsiGma™ coater.
- Loaded batch.
- Tablet ring (110–250 RPM, 75–95 °C).
- Cascade formation (88–110 RPM, 75–95 °C).
- Full “in flight” cascade (88–110 RPM, 75–95 °C).
A conventional spray nozzle is directed upwards into the cascade of “in-flight” tablets. The full surface area of each tablet is available to receive the coating on each pass. A high spray rate compared with the tablet charge is matched by high specific airflows. Filling and discharge is automated and rapid. The tablets are coated with the coating suspension in the same direction as the drying gas, resulting in a more efficient process. Owing to the coater's unique air distribution plate design, the tablets move quickly and predictably through the spray zone, receiving only a small amount of coating per pass and therefore achieving higher coating accuracy. The placement of the air knives both improves and regulates the cascade, ensuring that the coating suspension flows through the cloud of tablets; every tablet is exposed to the coating jet approximately 1.5 times a second and integrated “gripper bars” improve axial mixing.
Setting the tablets in flight means that they can be sprayed as discrete elements, benefiting from the wraparound effect of the droplets and evaporation from the entire surface. With enough evaporative heat, the process can be accelerated. By comparison, in conventional drum coating processes, only the exposed surface of the rolling bed can be sprayed and airflow is limited by the close proximity of other tablets. To optimize the process, the ConsiGma™ coater drum should be loaded with enough tablets to make a 20–25 mm deep bed once the ring stage has been reached. A single tablet would lack the traction to stick to the wall, for example, and a single or monolayer of tablets in cascade would allow too much spray to pass through the tablets and coat the drum and housing. Handling very small loads would involve a disproportionate of loading and discharging time when no spraying can take place. The tablets can be induced to fly at rotational speeds that are somewhat in excess of the theoretical critical speed because of factors such as air drag and energy loss owing to friction as the tablets jostle together, and the action of the two radial air knives on the rising side of the wheel before the take-off point allows the tablet cascade to be stabilized and ensures that the full bed depth is made mobile (tablets that do not enter the cascade do not get properly coated). Drying air is fed into the wheel along a hollow axis, passing through the annular tablet bed to maximise drying efficiency (they also contribute by increasing velocity gradients and recirculating air back into the wheel). The nozzle sprays upwards in to the tablet bed just after the point of take off to maximise deposition efficiency and in-flight drying time.
Thermodynamics: An intensified process requires a high heat transfer capability. Tablets must leave the coating process with no residual solvent (derived from the coating suspension). As such, specific air volumes are high: preheat and post-spraying drying times of 20–30 seconds are typical. The specific moisture content of the exhaust air is seen to rise rapidly to a plateau level at the start of spraying and fall equally rapidly at the end. The drying rate matches the rate of solvent addition (Figure 2).
Figure 2: Thermodynamic parameters of the ConsiGma™ coater in action.
The process time is comparatively short, taking seconds or minutes as opposed to hours, and is therefore gentler on the tablets and more cost effective. The coating process is, therefore, accurate and homogenous, resulting in an even coat with few defects and clearly defined intagliations. The ConsiGma™ enables the coating of friable and moisture-sensitive tablets, as well as flat or highly oblong tablet shapes. In fact, the ConsiGma™ will coat anything that a conventional system will, but is not restricted to particular core sizes or shapes. It will also operate with functional coatings, mini-tablets and caplets (500–600 mg).
Drying is very fast, making it possible to coat extremely hygroscopic tablets. The accuracy of deposition is great enough that active pharmaceutical ingredients (APIs) can be layered onto tablets, and uniform layers of taste masking or modified release coatings can be applied consecutively within a single continuous batch.
The ConsiGma™ coater can be operated as single or multiple modules; when matched to a GEA continuous tableting line for the application of immediate release coatings, two modules are generally used, delivering a throughput of up to 25 kg/h (Figure 3). This small-scale, agile production machine is multifunctional, easy to use and set up, and delivers the right results, first time and every time. As the coater can be linked directly to a tablet press or bulk container, it offers both gravimetric and volumetric feed options, rapid changeover (of the coating wheel, tablet hoppers and the entire module) and, as such, is easy to clean. The coating module (wheel in housing) can be removed on a purpose-built trolley and washed remotely. The inlet and discharge hoppers can be removed by hand.
Other features include a trapdoor in the periphery of the wheel that allows fast loading and discharge, and tablet air lock chambers (hoppers) on the feed and discharge that leave the process airflow undisturbed. In addition, the wheel can be reloaded while the discharge airlock is emptying and the exhaust air is cleaned in a twin blowback HEPA filter.
Figure 3: ConsiGma™ coater twin-wheel manufacturing unit.
The ConsiGma™ coater is PAT compatible, efficient — warm up and drying times are faster than conventional coaters — and reliable, delivering a consistent, homogenous and even tablet weight gain and coating distribution. And, because the coater operates at higher speeds and temperatures than other products on the market, higher spray rates and improved tablet mixing can be achieved, expanding its application potential to polymer coatings and beyond what is currently possible. It can even be used to dedust tablet cores prior to coating.
With more tablet movement within the coating barrel, the revolutionary design and the application of enhanced process conditions, the small-volume ConsiGma™ coater concentrates the tablet coating process, enabling faster throughput, time and cost savings, increased efficiency and a higher quality finished product, all of which are fundamental aspects of the drive towards continuous processing.
- Continuous coating
- Short processing time
- Flexible modular design
- R&D batch size (minimum batch size = XX g)
- Enhancing technology
- Difficult-to-coat shapes
- Friable tablets
- Multi-layer coating
- Enabling technology
- Low humidity process: suitable for moisture sensitive materials
- Accuracy of coating (RSD less than 1% demonstrated).