In the past two years, a new type of coating system, the fluidized bed bottom-injection precision coating system, has appeared on the production lines of some domestic pharmaceutical companies one after another. Professionals believe that it is expected to replace the traditional fluidized bed bottom spray coating system that has a history of more than 50 years. Compared with the traditional fluid bed bottom spray coating system, the precision coating system can better meet the needs of pharmaceutical companies for improving product yield, improving coating quality and reducing process time.
There are four shortcomings of the traditional bottom spray coating
The coating technology is varied, but the fluidized bed coating technology is also effective. It can be said that it is the "old man" of coating technology and has won the favor of pharmaceutical companies. One of the most commonly used is the Wurster bottom-jet fluidized bed developed by Dale Wurster in the 1960s. The device has a coating column in the center of the device and a fixed two-fluid nozzle for spraying the coating solution in the product bed, extending in the direction of the coating column. During the coating process, the coating solution rapidly passes through the coating column under the action of the atomizing air stream and is coated with the particles. The Wurster-type design has been used until now with no significant changes. Although the current system is still one of the main tools for fine particle coating, it has revealed obvious deficiencies in product yield, coating quality control, process time, and process magnification.
One is affecting product yield. The Wurster system is effective for coating particles having a particle size in the range of 0.4 to 1.2 mm, but the coating of particles having a particle size of less than 400 μm causes problems such as particle aggregation, uneven coating, and the like. Since the nozzle of the Wurster system is fixed on the air distribution plate of the fluidized bed and the nozzle head is higher than the distribution plate, once the nozzle is atomized and sprayed at a high speed, negative pressure is generated around the atomized lower area of ​​the nozzle, so that the adsorption particles are In this area, and because the area is close to the nozzle, the droplets are larger, and the particles are more likely to gather in the area. Some of the small clusters may eventually be blown, and the unqualified products that are not dried are eventually screened out. ; And large clumps may block the nozzle. In addition, the system is vertical intake, the particles move vertically upwards, lack of sufficient rotation movement, and the movement is relatively violent, the collision friction between the particles is fierce, so some particles may be crashed into fine powder - these will affect Product yield.
The second is that the coating quality is difficult to control. Since the inlet flow of the traditional Wurster system is vertical, in each cycle, only the lower surface of the particles is sprayed with the coating solution. Therefore, spraying can be guaranteed only by repeating the cycle and strictly controlling the regularity of the particle appearance. Uniformity. In addition, the nozzle in the Wurster system is located in the middle of the particle stream, which means that the wet particles may stick to the nozzle, causing the coating solution to not fully expand, and only part of the particles close to the nozzle can uniformly coat, so the quality of the coating It's hard to control. In addition, the Wurster system's spray gun is fixed on the air distribution plate of the fluidized bed. Under the effect of negative pressure, the nozzle is easily blocked. Once the nozzle is blocked, the fluidization must be stopped. The material must be shut down to check and clean the nozzle. After that, the production can be re-injected. In severe cases, the whole batch may be scrapped.
The third is the long time for coating. In the Wurster system, about 25% to 30% of the fluidized air enters the product bed area to help the particles move to the coating column, where the air volume directly through the drying zone of the coating column is only 70% to 75%, due to the dry air The utilization rate is too low, resulting in longer coating times.
The fourth is the difficulty of process amplification. Because the air intake of the Wurster system is vertically upward, the air volume is unevenly distributed throughout the intake cavity. When the single-column multi-column is used for production amplification, the particles may not be uniformly moved in the bed and affect the quality of the final product. .
Three aspects of precision coating system design
In response to the shortcomings of traditional under-bed fluidized bed coating systems, some companies at home and abroad have turned their sights to the highly advantageous new coating technology—precise coating. There are three points in the design of the precision coating system: First, it has a patented airflow spinner. The device is located underneath each coating column, and its specially designed rotating blades can make the tangential inlet air flow be secondary distribution to form a rotating airflow.
This swirling airflow allows the particles to be coated while being rotated and raised. As the particles pass through the guide drum, the particles with upward power are in fact coated at the bottom of the coating column because the bottom pressure is low. In each cycle, all the outer surfaces of a rotating particle have equal access to the coating liquid, so the coating is very uniform and the coating quality is greatly improved. In addition, due to the spin action, the chances of collisions and adhesions between the particles to form agglomerates are greatly reduced, and the yield is naturally improved.
The second key to the design is the air distribution plate. Above it is a 0.7 mm diameter hole with an open porosity of 0.5% to 3%. This structure can play a role in buffering the particles before entering the coating column. The farther away from the coated column, the higher the open rate, up to 3%; the closer to the coating column, the open rate drops sharply to 0. This creates a pressure difference in the product bed that moves the product toward the center. In the conventional Wurster system, about 25% to 30% of the fluidized air enters the product bed area to help the particles move into the coating column; in the precision coating system, only 10% of the air volume is required The particles are moved into the coating column. Obviously, the precision coating system is about 20% higher than the Wurster system in terms of air utilization rate; the spray rate can be increased by 20% compared to the Wurster system while ensuring the same amount of air intake. This means that the former can save 20% of production time.
The third key to the design is that the spray gun of the precision coating system enters the fluidized bed in the form of a hose, which is a huge reform compared with the traditional design. The production personnel can inspect the nozzle at any stage without stopping the machine; even if it is blocked, the spray gun can be withdrawn and the nozzle can be cleaned while keeping the particles fluidized. The traditional Wurster system needs to stop fluidization, which may lead to a decline in product quality or even scrapping the entire batch.
Based on these characteristics of the precision coating system structure, compared with the traditional Wurster coating system, it has more significant advantages in production amplification. Due to the inhomogeneity of the intake air in the conventional Wurster system, particle movement is disordered, and it is necessary to re-explore it according to the actual situation during scale-up production. The precision coating system has an air distribution plate, which has a certain open rate at a location away from the coating column; in addition, the air accelerator is located below the coating column and can direct air into the column and pass through. The blades change the direction of gas flow and create a swirling vortex. These structures allow the particles to easily pass through the coating column into the surrounding bed, and the movement of the product at each coating column is uniform. If you need to scale up production, the relevant parameters (such as spray rate, air flow) are consistent with the experimental model data.
There are four shortcomings of the traditional bottom spray coating
The coating technology is varied, but the fluidized bed coating technology is also effective. It can be said that it is the "old man" of coating technology and has won the favor of pharmaceutical companies. One of the most commonly used is the Wurster bottom-jet fluidized bed developed by Dale Wurster in the 1960s. The device has a coating column in the center of the device and a fixed two-fluid nozzle for spraying the coating solution in the product bed, extending in the direction of the coating column. During the coating process, the coating solution rapidly passes through the coating column under the action of the atomizing air stream and is coated with the particles. The Wurster-type design has been used until now with no significant changes. Although the current system is still one of the main tools for fine particle coating, it has revealed obvious deficiencies in product yield, coating quality control, process time, and process magnification.
One is affecting product yield. The Wurster system is effective for coating particles having a particle size in the range of 0.4 to 1.2 mm, but the coating of particles having a particle size of less than 400 μm causes problems such as particle aggregation, uneven coating, and the like. Since the nozzle of the Wurster system is fixed on the air distribution plate of the fluidized bed and the nozzle head is higher than the distribution plate, once the nozzle is atomized and sprayed at a high speed, negative pressure is generated around the atomized lower area of ​​the nozzle, so that the adsorption particles are In this area, and because the area is close to the nozzle, the droplets are larger, and the particles are more likely to gather in the area. Some of the small clusters may eventually be blown, and the unqualified products that are not dried are eventually screened out. ; And large clumps may block the nozzle. In addition, the system is vertical intake, the particles move vertically upwards, lack of sufficient rotation movement, and the movement is relatively violent, the collision friction between the particles is fierce, so some particles may be crashed into fine powder - these will affect Product yield.
The second is that the coating quality is difficult to control. Since the inlet flow of the traditional Wurster system is vertical, in each cycle, only the lower surface of the particles is sprayed with the coating solution. Therefore, spraying can be guaranteed only by repeating the cycle and strictly controlling the regularity of the particle appearance. Uniformity. In addition, the nozzle in the Wurster system is located in the middle of the particle stream, which means that the wet particles may stick to the nozzle, causing the coating solution to not fully expand, and only part of the particles close to the nozzle can uniformly coat, so the quality of the coating It's hard to control. In addition, the Wurster system's spray gun is fixed on the air distribution plate of the fluidized bed. Under the effect of negative pressure, the nozzle is easily blocked. Once the nozzle is blocked, the fluidization must be stopped. The material must be shut down to check and clean the nozzle. After that, the production can be re-injected. In severe cases, the whole batch may be scrapped.
The third is the long time for coating. In the Wurster system, about 25% to 30% of the fluidized air enters the product bed area to help the particles move to the coating column, where the air volume directly through the drying zone of the coating column is only 70% to 75%, due to the dry air The utilization rate is too low, resulting in longer coating times.
The fourth is the difficulty of process amplification. Because the air intake of the Wurster system is vertically upward, the air volume is unevenly distributed throughout the intake cavity. When the single-column multi-column is used for production amplification, the particles may not be uniformly moved in the bed and affect the quality of the final product. .
Three aspects of precision coating system design
In response to the shortcomings of traditional under-bed fluidized bed coating systems, some companies at home and abroad have turned their sights to the highly advantageous new coating technology—precise coating. There are three points in the design of the precision coating system: First, it has a patented airflow spinner. The device is located underneath each coating column, and its specially designed rotating blades can make the tangential inlet air flow be secondary distribution to form a rotating airflow.
This swirling airflow allows the particles to be coated while being rotated and raised. As the particles pass through the guide drum, the particles with upward power are in fact coated at the bottom of the coating column because the bottom pressure is low. In each cycle, all the outer surfaces of a rotating particle have equal access to the coating liquid, so the coating is very uniform and the coating quality is greatly improved. In addition, due to the spin action, the chances of collisions and adhesions between the particles to form agglomerates are greatly reduced, and the yield is naturally improved.
The second key to the design is the air distribution plate. Above it is a 0.7 mm diameter hole with an open porosity of 0.5% to 3%. This structure can play a role in buffering the particles before entering the coating column. The farther away from the coated column, the higher the open rate, up to 3%; the closer to the coating column, the open rate drops sharply to 0. This creates a pressure difference in the product bed that moves the product toward the center. In the conventional Wurster system, about 25% to 30% of the fluidized air enters the product bed area to help the particles move into the coating column; in the precision coating system, only 10% of the air volume is required The particles are moved into the coating column. Obviously, the precision coating system is about 20% higher than the Wurster system in terms of air utilization rate; the spray rate can be increased by 20% compared to the Wurster system while ensuring the same amount of air intake. This means that the former can save 20% of production time.
The third key to the design is that the spray gun of the precision coating system enters the fluidized bed in the form of a hose, which is a huge reform compared with the traditional design. The production personnel can inspect the nozzle at any stage without stopping the machine; even if it is blocked, the spray gun can be withdrawn and the nozzle can be cleaned while keeping the particles fluidized. The traditional Wurster system needs to stop fluidization, which may lead to a decline in product quality or even scrapping the entire batch.
Based on these characteristics of the precision coating system structure, compared with the traditional Wurster coating system, it has more significant advantages in production amplification. Due to the inhomogeneity of the intake air in the conventional Wurster system, particle movement is disordered, and it is necessary to re-explore it according to the actual situation during scale-up production. The precision coating system has an air distribution plate, which has a certain open rate at a location away from the coating column; in addition, the air accelerator is located below the coating column and can direct air into the column and pass through. The blades change the direction of gas flow and create a swirling vortex. These structures allow the particles to easily pass through the coating column into the surrounding bed, and the movement of the product at each coating column is uniform. If you need to scale up production, the relevant parameters (such as spray rate, air flow) are consistent with the experimental model data.
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