Tablet coating machines have become an essential part of the pharmaceutical industry. They offer better protection for the tablet and an improved customer experience.
However, before you can invest in a machine, you need to understand the differences in how they coat your tablets.
What A Tablet Coating Machine Does
To maximize the benefits offered by tablet coating machines, it’s essential that all the tablets are coated evenly. High-quality machines automate this process to ensure it is completed quickly and effectively.
Although there are several different types of tablet coating machines, they all use pans or drums to contain the tablets. In addition, nozzles are fitted inside, allowing control over the quantity of coating sprayed into the drum. Hot air is directed around the chamber to ensure the coating dries evenly.
Types Of Tablet Coating Machines
Although there are many different tablet coating machines on the market, all the machines use one of the following three principles.
Fluidized Bed
Fluidized bed coating machines are generally agreed to be the most efficient. The coating is sprayed onto the tablets. However, before this happens the tablets are held in a warm airflow.
This type is also known as an air suspension system. The machine is carefully calibrated to ensure the majority of the air enters in the middle of the machine. The tablets are put in the chamber and, thanks to the increased airflow in the center, the tablets will move into the center of the chamber. As the warm air lifts them up through the chamber they are sprayed with the coating solution.
Some machines spray across the tablet from the lower part of the chamber, and others spray from the top, cascading down over the tablets. A top spray is generally considered the more effective model.
What makes this system particularly efficient is that, when the tablets reach the top, they gently fall back down and then rise up through the centre of the machine again. This ensures a complete and even coating.
It’s worth noting that fragile tablets can’t be coated in this way. Because the tablets are easily damaged, the continual movement and bumping will chip the edges of the tablets, reducing the amount of medication available, and damaging the tablet.
This type of fluidized bed system can be separated into two options:
High-pressure Systems
The high-pressure system is prevalent when it comes to coating multi-particulate systems. As the name suggests the spray guns used to coat the tablets emit fine particles of spray under high pressure.
This helps to ensure every tablet is evenly coated.
Of course, the higher the pressure the smaller the droplets. That’s why high-pressure systems are generally used with higher-viscosity solutions.
These types of systems are airless, which can make it difficult to control the application rate. The pressure is generally between 250-3000 psig, and the coating is distributed through a nozzle between 0.009 and 0.2 inches.
Perhaps the biggest issue with this type of system is that the orifice can be easily blocked which will damage the flow of coating and potentially cause production issues.
Low-pressure Systems
Low-pressure systems are the preferred choice when using low-viscosity solutions. These are normally applied at between 5-50 psig and the delivery orifices are between 0.020 and 0.06 inches.
This coating is particularly useful when you need to control the system atomization separately from the pressure in the operating system. The result is a very fine spray that encourages even distribution across the surface of the tablet.
Low-pressure tablet coating systems are often referred to as air-atomizing systems.
The major difference between these two types of systems is that high-pressure systems atomize the coating before it is pumped out of the nozzles. Low-pressure systems atomize as the coating leaves the nozzle using a blast of compressed air.
In general high-pressure systems are used when coating tablets on a large scale, ideally with organic-based coatings. In contrast, the low-pressure system is better with small-scale operations and aqueous coatings.
Standard Coating Pan
This type of tablet coating machine has a circular metal pan. The pan can have a diameter of anything between eight and 60 inches. It’s attached at a slight angle to a stand, allowing it to rotate. The speed of the rotation can be controlled depending on what coating is being applied.
As the pan rotates, the tablets will rise and then fall back to the bottom of the pan. This ensures every tablet passes through the spray zone on multiple occasions. It effectively ensures an even coating.
To improve the speed and evenness of the coating, this type of machine often sprays the tablet coating in an atomized form.
To assist the coating drying and sticking to the tablets hot air is introduced to the pan via a centrally-positioned air duct. A secondary duct acts as an exhaust to remove the excess air.
While the basic system is effective, there are variants which are more efficient at drying the coating and, therefore, ensuring an even application.
Immersion Systems
There are two types of immersion systems. The first is an immersion sword system. It literally has a perforated metal piece, shaped like a sword, built into the base of the pan. Hot air comes through this ‘sword’ to dry the tablets faster and more efficiently.
The alternative is an immersion tube system. This utilizes a tube that ends on the tablet bed. At the tip of this tube, there is a small nozzle which directs hot air into the tablet bed, helping to dry the tablets faster.
Pellegrini Pan System
The Pellegrini pan system uses a baffled pan and diffuser. The diffuser crosses through the middle of the pan. It should be noted that the pan has tapered side walls to aid the distribution of tablets.
This helps to ensure the hot air is evenly dispersed across the pan and the tablets.
While the Pellegrini pan system is very effective it’s only used when applying sugar coatings. It can’t offer an efficient drying process for film coatings.
Perforated Coating Pan
The perforated pan system also uses a drum attached to a stand which rotates on an axis. This drum is usually enclosed and there are perforations across the drum. A series of nozzles are fitted inside the drum, allowing the coating to be sprayed onto the tablets while the drum rotates.
This type of coating machine became popular when aqueous coatings started to become more popular than organic solvent-based ones. In essence, the machines were cheaper and more efficient as they didn’t need the explosion-proof casings associated with organic solvent volatility
There are a variety of perforated pan designs:
Accela Cota System
The pan perforations in this system allow the hot air to exit the drum. The air is pumped into the drum via a central tube.
Dumoulin Coating System
The Dumoulin coating system is best used for sugar-based coatings. The coating is introduced via a set of spraying nozzles near the base of the enclosed drum. The lining of the drum has ribs to keep the tablets moving. The air temperature inside the drum is carefully controlled to maximize drying time.
This system is most commonly used for sugar coatings.
Glatt Pan System
This coating system relies on fully perforated drums. Again, the drum is fully enclosed. As the drum spins, hot air is directed into the bottom of the chamber. The coating is sprayed from downward-facing jets located in the center of the drum. The air is then removed via a duct at the top of the drum.
It’s possible to adjust the airflow in and out depending on what coatings you are applying.
Hi-coater System
This system works in a similar way to the accela cota design. The drum is enclosed with tapered edges. The base of the pan has a perforated plate and the tablets sit above it.
Hot air is driven into the drum from one side entering above the plate and below the overhead jets directing the coating into the space. As the hot air cools it drops through the perforated plate and leaves on the other side of the drum.
Dria Coater System
In this case, hot air is introduced through perforated ribs which sit inside the drum. As the pan rotates the tablets dip in and out of the ribs. The hot air dries the tablet coating and then exits through the back of the drum.
Factors To Consider When Choosing A Tablet Coating Machine
Before you select a tablet coating machine, consider the following.
Production Level
Before choosing any machine you need to consider how big, or small, each batch will be and how long you want to take producing each batch. This will directly affect the size and even the type of machine you choose.
Don’t forget to consider your anticipated growth.
Machine Type
As shown above, there are several different types of machines. All are effective at coating tablets. However, some are better designed for sugar coatings, smaller batches, speed of drying, etc.
Consider which type meets your needs, it will make your decision easier.
Features
Some machines are fully automated, others partially, and some can be adjusted to suit your needs. The choice regarding which system is best is usually guided by the amount of control you need over the coating process, quality, and even the ability to troubleshoot issues.
Other features worth considering are how the machine is configured and which type of heating/drying system it uses.
Available Space
Coating machines vary greatly in size. Assess the production area you have before choosing a machine. This will ensure the machine fits and can be added smoothly into your production process.
Conclusion
Understanding the different types of coating machines is essential if you’re going to choose the right one for your business.
You’ve learned about the various options available, now it’s time to put what you’ve learned into practice.
Saintytec offers a selection of state-of-the-art tablet coating machines which are cGMP compliant. We specialize in perforated pan coating systems and can help you decide which one is best suited to your requirements. Talk to us today, we’ll help you place your order and see the difference it will make to your business.