Fluidized Bed Spray Coating: The Complete FAQ Guide In 2024

1.What Is Pellet?

What Is Pellet-sourced: iptonline

Pellet generally refers to a micro-preparation with a diameter of less than 2.5mm. It is often used in various capsule fillings, tablet production or added to suspensions.

Benefits of pellets are:

• Not affected by food category;
• Short stay time in the gastrointestinal tract;
• Evenly dispersed and convenient for gastrointestinal absorption;
• Little irritation to the gastrointestinal tract;

Benefits of pellets-sourced: hoefliger

The most representative micro-pellet preparation on the market now is the ibuprofen sustained-release capsule developed by GlaxoSmithKline in 1952. It mainly uses the process of fluidized bed spray coating to make the pellet core do centrifugal movement in the equipment, and then sprays adhesives and required materials to make the pellet core grow continuously and finally form pellets.

2.What Is Fluidized Bed Spray Coating For Pellets?

What Is Fluidized Bed Spray Coating For Pellets-sourced: foodfeedfinechemicals

The fluidized bed spray coating, also called as Wurster coating, is a coating mainly used for pellets. It was first patented by Wurster in 1959. Unlike top spray granulation, the spray gun of the fluidized bed spray is located at the bottom of the fluidized bed.

By utilizing drying, granulation and coating technologies, it can coat carefully formulated materials onto different materials by atomization, thereby achieving good coating and drying effects.

3.What Is The Regular Coating Principle?

Regular Coating Principle of AIPAK PHARMA tablet coating machine

Regular coating, also called as regular tablet coating, is a process that mainly decomposes the coating liquid into small droplets under the action of atomized air, and then the coating machine evenly sprays the small droplets on the surface of the pill core. This coating material can form a thin film on the surface of the tablet.

Its main processes include minimum temperature film formation, glass transition temperature, spray drying, mass conservation, dry air, etc. Its technology is slightly simpler. It is easier to implement and the equipment involved is also simpler.

4.What Is The Fluidized Bed Spray Coating Principle?

Unlike regular coating systems, the spray gun of the fluidized bed spray coating system is located at the bottom of the airflow plate. Its working principle is as follows:

What Is The Fluidized Bed Spray Coating Principle-sourced: glatt

• There is a large guide tube inside the fluidized bed. When the micro-pills enter the guide tube, high-speed airflow will automatically begin to be generated inside;
• When the micro-pills are subjected to air resistance greater than their own gravity in the guide tube, they will be lifted upward along the wall of the guide tube under the influence of high-speed airflow;
• During the lifting process, the spray guns distributed at the bottom of the fluidized bed will spray the coating liquid evenly;
• The lifted micro-pills will automatically enter the spraying area and be evenly coated with the coating liquid;
• The micro-pills evenly coated with the coating liquid gradually become larger, and under the influence of their own gravity, they begin to spread around along the guide tube and away from the spraying area;
• Therefore, the micro-pills that have not been coated at the back are lifted again under the influence of airflow and return to the spraying area;
• This cycle repeats until all the micro-pills are evenly coated with the coating liquid.

5.What Is The Fluidized Bed Spray Coating System?

What Is The Fluidized Bed Spray Coating System-sourced: glatt

The fluidized bed spray coating system includes air inlet system, exhaust system, material chamber, drying chamber, filter chamber, guide tube, etc.

Air inlet system

The air inlet system is located at the bottom of the entire chamber. It can introduce controlled high-temperature airflow into the atomization and drying chamber. And then it can ensure that your material is evenly fluidized and dried.

Material chamber

The material chamber is usually designed in a V-shaped or H-shaped shape. The design principle is to ensure that the wind speed will decrease as the cavity area increases, or when the upper and lower areas of the cavity are the same, the wind speed in the cavity will remain constant. By controlling the wind speed, the friction loss of the pellets is minimized.

Drying chamber

With the same design principle as the material chamber, the V-shaped or H-shaped shape design can ensure that the material in the cavity is evenly dried without any loss while pursuing large capacity. When the material falls in the cavity, it can have a greater buffering force.

Filter chamber

Also known as the fluidized bed filter, it can filter suspended particulate matter through airflow. This helps the uniform atomization of the subsequent materials.

Guide tube

Each fluidized bed spray coating system needs to be equipped with a guide tube. If you want to increase your production, you can directly increase the number of guide tubes. The number of guide tubes you can choose and install is 3, 6 or 7.

6.What Is The Fluidized Bed Spray System?

What Is The Fluidized Bed Spray System-sourced: glatt

Compared with ordinary tablet coating systems, the bottom spray coating process of the fluidized bed spray system is longer and more complicated, and takes longer, which may take about 2-3 days. The whole process of the fluidized bed spray system is:

The whole process of the fluidized bed spray system-sourced: glatt

• Maintain a dynamic balance between the air volume, air temperature and spray speed;
• If you want to increase the drying speed of the material, you can increase the air volume and the temperature of the air inlet, etc.;
• To maintain the efficiency and temperature of material drying, you can increase the spray speed to increase the coating speed;
• The speed of the bottom spray coating liquid is controlled by controlling high-speed compressed air. When compressed air passes through the nozzle, the negative pressure will suck the coating liquid out of the nozzle;
• When sucking out the coating liquid, the micro-particles may also be adsorbed on the nozzle;
• To prevent the micro-particles from sticking, you can optimize the coating speed;
• By adding a sleeve around the bottom spray gun, the micro-particles and the negative pressure area of the spray gun are isolated, so that the micro-particles can be prevented from sticking, etc.;
• Or you can use a spray gun with a sleeve. This sleeve does not contain air.

7.Are There Other Coating Equipment For Your Need?

Romaco fluidized process bed

Unlike other types of coating equipment, Romaco can provide you with a perfect bottom spray coating solution in bottom spray coating equipment. Compared with ordinary bottom spray coating equipment, fluidized bed spray system can provide you with a denser film, faster coating speed and greater output. Its features are:

Controlled air intake system

Controlled air intake system-sourced: romaco

The chassis of the air intake system of fluidized bed spray system has been redesigned and improved. It is composed of guide rings of multiple sizes. When the moving air flows into the fluidized bed through the gap between the rings, the guide grooves at the tangential angle can ensure that your air intake volume and speed are controlled.

Rotary spray gun

Rotary spray gun-sourced: romaco

The rotary spray gun can ensure that the pellets reach the suspension height after being affected by the rising air flow, and when the buoyancy is reduced and then falls by gravity, they can move in a spiral trajectory. This can ensure the best atomization effect.

Top spray mode

Unlike the previous top spray mode, the rotary spray gun adopts the bottom spray gun mode. It can provide your material with a three-layer gap coating liquid atomization on the side ring surface. And it has an internal rotating rotor inside, which can handle the material that has not been dried in time and is stuck at the nozzle.

Non-porous coating effect

In addition to achieving the drying function, ordinary coating machines can also achieve the purpose of material fluidization at the same time. The Romaco fluidized bed spray system is more responsible for drying. Its base is solid and safe, with strong support, and can provide you with efficient coating effects.

8.What Are The Important Related Parameters Of Fluidized Bed Spray Coating?

Fluidized bed spray coating machine includes two parts: fluidized bed granulation and tablet coating. The variables that need to be paid attention to in these two parts mainly include inlet air temperature, inlet air volume, spray speed, material temperature, atomization effect, etc. If there is a problem in one of the links, it may affect the overall coating and drying effect.

Important Related Parameters Of Fluidized Bed Spray Coating-sourced: researchgate

The important related parameters of fluidized bed spray coating are:

Material temperature

The temperature of the material should be well controlled. Too high temperature is easy to break and lose, too low temperature is easy to be unformed and uneven coating.

Inlet air temperature

The inlet air temperature of Fluidized bed spray coating is generally kept at 40-80°C. If a higher temperature is used to enhance the drying effect, the activity of sensitive components in the adhesive and material may be damaged.

Inlet air volume

The more stable the inlet air volume, the better the atomization effect. If the inlet air volume speed is not well controlled, the atomization effect may deteriorate.

Spray speed

If there is no production regulation, the generally adjustable spray speed is 5-100 g/min. The faster the spray speed, the easier it is to refine the atomized coating effect of the material. On the contrary, the slower the speed, the easier it is to cause material agglomeration and uneven atomization.

Atomization air pressure

The finer the atomized droplets, the more uniform the coating can be. Generally, if you want to improve the quality of atomization, you can increase the atomization air pressure.

Nozzle configuration

In addition to being able to choose top spray and bottom spray modes, in order to improve the efficiency of atomization, you can choose top spray, bottom spray and tangential spray at the same time. And you can increase the efficiency by increasing the number of nozzles.

Adhesive concentration

The adhesive concentration is determined according to your material and the atomization effect. If you need a better atomization effect, you can increase the adhesive concentration appropriately.

The regular range of parameters of fluidized bed spray coating are:

Bottom spray equipment size	Effective working volume	Air flow distribution plate area	Inlet air volume (example)	Spray rate (example)	Batch (example)
6"	3.5	0.019	75	10
7"	5.4	0.025	100	13.4	3
8"	14	0.042	160	21.9
9"	38	0.017	280	37.2
12"	102	0.156	610	81.9	40
18"	190
24"	417	0.522	2050	274.6
32"	820	1.094	4300	575.6	200
46"	3.5	0.019	75	10	400

9.What Effect Do Material Temperature And Solid Content Have On Fluidized Bed Spray Coating?

In the study of key parameters, material temperature, solid content, and coating weight gain are crucial. Their effects on fluidized bed spray coating include:

Effect of material temperature

Effect of material temperature

The normal tablet coating temperature is about 28 to 32 degrees Celsius. This temperature is also used as a reference temperature for enteric coating. However, the bottom spray coating is different from ordinary coating. Its material temperature should be bench-marked against the temperature of the drying stage, not the spraying stage.

Therefore, in the subsequent testing process, if your material temperature requirement is 28 to 32 degrees Celsius, you may test the two ranges of 20 to 25 degrees Celsius and 35 to 40 degrees Celsius.

Effect of solid content

The bottom spray coating of pellets is a process of combining solids and liquids. It requires your coating solution to be processed to be uniform, bubble-free, silky, non-sticky, non-precipitated, and the configuration process is smooth. To achieve this effect, the solid content concentration of the coating solution should be around 15%. However, an applicable concentration of 12% to 20% is also acceptable.

Coating weight gain

Coating weight gain

pellets are the perfect solution for controlled drug release. Therefore, some pellets can even achieve the effect of 6 layers of coating. Ordinary enteric tablets are coated with 1 to 2 layers, namely the isolation layer and the enteric layer. Functional pellets may include an isolation layer, an enteric layer and a controlled release layer, and the corresponding thickness is also required. The weight gain of the coating is controlled by the thickness.

The control relationship between coating weight gain and thickness is:

For every 20 micron increase in the coating thickness of the micro-pellet, when the micro-pellet diameter is 300 microns, the coating of the micro-pellet will increase by about 45%;

When the micro-pellet diameter is 500 microns, the coating will increase by about 30%;

When the micro-pellet diameter is 1000 microns, the coating will increase by about 13%;

10.What Are The Non-critical Parameters Of Fluidized Bed Spray Coating?

Some non-critical parameters are also worth paying attention to. They include: atomization pressure, bed pressure difference, filter screen, filter bag pore size, material loading, guide tube height, distribution plate pore size distribution, etc.

Atomization air pressure

Atomization air pressure

Atomization pressure can control the dispersion of coating liquid. General atomization pressure can disperse the coating liquid into particles less than 30 microns. The finer the atomization effect, the better the coating effect. However, too much atomization pressure can easily cause the coating liquid to fly and reduce the coating efficiency. For general pellets, it is best to control the atomization pressure at 0.1-0.2mPa.

Bed pressure difference, filter screen, filter bag pore size

Bed pressure difference, filter screen, filter bag pore size

The coating rate of ordinary wear-resistant pellets is basically about 95%. If you choose non-wear-resistant pellets, then its bed pressure difference is basically not a problem. In order to reduce the resistance of the filter screen or filter bag, the larger the pore size of your pellets, the better.

Material loading

The loading of bottom spray coating should not be too small. Generally, the ideal material loading is about 50% to 85%. In addition, you can calculate according to the size of your equipment and the density of the pellets:

Maximum batch = effective working volume * pellet finished product bulk density

Minimum batch = effective working volume * pellet finished product bulk density * 20~25%

The data of relevant equipment size and effective working volume are:

Equipment size	6”	7”	9”	12”	18”	24”	32”	46”
Effective working volume	3.5L	5.4L	14L	38L	102L	190L	417L	820L

Height of the guide tube

Height of the guide tube

The height of the guide tube refers to the placement height of the guide tube. This height needs to refer to the height of the tablet coating spray gun. The purpose of setting this height is to control the speed of the pellets from the descending bed to the ascending bed.

The higher the height is set, the more materials will enter the spraying area. The lower the height is set, the less materials will enter the spraying area. Generally, the reference height is: 15-25mm for experimental type; 30-60mm for production type.

Aperture distribution of distribution plate

Aperture distribution of distribution plate

Determine the aperture of the distribution plate by determining the size of the pellets you need. The larger the pellets, the larger the rising airflow required. Otherwise, it is easy to leak when adding materials. Therefore, the aperture of the distribution plate must be smaller than the diameter of the pellets.

11.What Is Pellets Scale-Up After The Fluidized Bed Spray Coating?

To enlarge the pellets, we need to compare several key parameters to analyze the effect of bottom spray coating. It includes:

Coating film quality and thickness

Coating film quality and thickness

During the bottom spray coating process, the material temperature will affect the film quality of the coating film, and the coating weight gain will affect the coating layer thickness. By comparing the two parameters of material temperature and coating weight gain, you can grasp the approximate coating quality.

Atomization effect

By comparing the inlet air temperature and the spray speed, you can get the relevant atomization effect. Too high a flow rate may have an adverse effect on the atomization effect. If the atomization effect is not ideal, you can also reduce the temperature of the material appropriately.

Preparation and stability of coating solution

Because the coating time of the pellets is particularly long, you need to pay special attention to the preparation and stability of the coating solution. You can observe and study the changes in its properties, viscosity, microorganisms and other test items after leaving the coating solution for 0, 24h, 48h, and 72h, and you can get relevant results.

12.What Is Process Validation Of Fluidized Bed Spray Coating?

Process Validation Of Fluidized Bed Spray Coating-sourced: testlodge

The process of fluidized spray coating has been developed very maturely. Except for the impact of the operation process, its overall risk is very small. Its process verification includes:

• Check whether the material temperature and coating weight gain meet the standards;
• Check whether the quality attributes of the micro-pellets are consistent;
• Collect operating parameters such as inlet air temperature, inlet air volume, and material temperature;
• Collect result indicators such as drug application rate (coating efficiency), coating weight gain, and yield;
• Inspect the mixing uniformity of micro-pellets in each layer of the pot;
• Inspect the storage stability of each layer of coating solution;

Conclusion:

The fluidized bed process system and fluidized bed spray coating can be applied to all powder processing. Whether it is a laboratory or a factory, a fluidized bed spray coating system is needed. This complete FAQ guide of fluidized bed spray coating have explained clearly about the top spray technology. If you want to take a try for the new formulations, please do not hesitate to contact ALLPACK now!