Abstract: Starting from the concept of fluidized bed coating technology, this article evaluates and analyzes the pharmaceutical negative pressure bottom spray fluidized bed coating machine of Jiafa Company, with the aim of enabling pharmaceutical users to have a more systematic understanding of the bottom spray fluidized bed coating machine.

Keywords: fluidized bed coating; Medical negative pressure bottom spraying fluidized bed coating machine; Evaluation and Analysis

　　A trend in the development of drugs worldwide is towards drugs such as sustained-release and controlled release. Due to the immaturity of such technologies and equipment in previous years, the development of drugs such as sustained-release and controlled release has been slow. However, in recent years, through the research and development of pellets (granules) coating technology and equipment, various types of pellets (granules) coating equipment have emerged, which has also driven the continuous development of drugs such as sustained-release and controlled release in China. Among them, the bottom spray fluidized bed coating machine is one of the successful equipment. The author will start with the concept of fluidized bed coating technology and evaluate Jiafa Company's pharmaceutical negative pressure bottom spray fluidized bed coating machine. The aim is to enable such equipment to make greater contributions to the development and production of drugs such as slow and controlled release in China, and also to enable pharmaceutical users to have a more systematic understanding of the bottom spray fluidized bed coating machine.

1. From the "bottom spray" of fluidized bed coating technology

　　Fluidized bed coating is a process in which all particles are suspended in the fluidized airflow, with the surface completely exposed, and various coating liquids can be sprayed and subjected to moisture and heat exchange. The fluidization state is determined by the characteristics of the fluidized materials and the structure of the equipment. Because each technology is different, its fluidization state is also different. There are often three spray technologies for coating, namely top spray, bottom spray and side spray. In order to make the coating film even and continuous, try to reduce the stroke of the droplets (that is, the distance of the droplets from the nozzle outlet to the particle surface), so as to reduce the spray drying effect of hot air on the droplets, so that when the droplets reach the surface of the coated particles, their original characteristics can be basically maintained, so as to achieve uniformity, ideal spread and continuity of the coating film. A comparison is made between top spray, bottom spray, and side spray fluidized beds:

(1) The top spray fluidized bed usually has a conical material groove, with the spray gun at its highest position. The fluidized airflow enters the material groove through the bottom sieve, and as the airflow rate increases, the original stationary material is pushed by the airflow to fluidize. Its particles are accelerated from the material groove by the airflow and pass through the nozzle. The nozzle sprays coating liquid onto the surface of irregularly moving particles, which is opposite to the direction of particle movement.

(2) A atomizer is installed in the center of the bottom spray fluidized bed distribution plate, and a circular guide tube is installed in the center of the material bed with an expansion chamber. The distribution plate has a large opening rate in the guide tube area to meet the passage of most of the air flow, forming a fountain like fluidization. The powder particles accelerate from the air flow inside the guide tube and then leave the guide tube to enter the expansion chamber, Subsequently, the rapid decrease in wind speed causes the material to fall into the annular gap area between the bed and the guide tube, resulting in a high degree of dispersion of the material.

(3) The side spray fluidized bed material tank is cylindrical, with a variable speed rotating plate at the bottom. The rotating plate can move up and down to adjust the intake volume, and the coating liquid is sprayed into the material tank through the atomizing nozzle on the wall of the material tank. The spraying direction of the nozzle is consistent with the direction of particle fluidization, and the coating liquid is tangential sprayed into the material tank. The movement of particles in the material trough is spiral, uniform, and orderly, and three forces are combined.

　　For top spray, bottom spray and side spray, the three spray methods have their own characteristics in fluidized bed coating. Their comparison is shown in Table 1. It can be seen that the spray type is the bed type most suitable for pellet (pellet) coating.

2. Characteristics of bottom spray fluidized bed coating machine

　　The bottom spraying fluidized bed coating was founded by Dr. Dale Wurster of the University of Wisconsin in 1959. The combination of spouting fluidization and spray forms a fountain state, which makes industrial coating practical. Its technology has been widely used so far, and no other form can compare with it. Its characteristics are:

(1) Spraying liquid in the same direction causes the direction of spraying liquid to be consistent with the direction of particle movement, exhibiting the characteristics of fast, continuous, and uniform;

(2) The coating liquid is sprayed on the surface of particles that move in an orderly manner near the nozzle, so the distance between the droplets and the surface of the coated particles is very short, making it easy to form a continuous and tight coating film. The quality of the coated film is good.