Talking about Powder Granulation and Coating (Part 1)

Whether it is medicine, food, new energy materials, ceramics, or chemical industry, they are all processes from raw materials to finished products, which can be seen as the path of "API ->formulation". However, due to the specificity of different fields, the processes used from raw materials to finished products have not been integrated and connected. After being exposed to various industries and applications, I pondered and found many similarities. If we learn from the technological methods of other industries, it may have a very good effect.

Burial is a very interesting topic.

In the pharmaceutical industry, tablet coating is the most common form of embedding. The commonly used micro pill coating for sustained-release formulations, which involves the blank pill core sequentially encapsulating the drug loading layer, isolation layer, and enteric coating layer, is also a typical application. In the past two years, the track of developing children's drugs and fine-grained formulations suitable for swallowing difficulties has also been quite hot. When the preparation roll is not needed, some companies roll it up from the source and modify the API through solid dispersion or embedding to improve the flowability and dissolution of raw materials, facilitate subsequent preparation production, and enhance bioavailability. In the above application process, the transformation of the embedded object from large to small requires the use of different process equipment to achieve. Tablets are coated with a coating machine, while pellets/granules are coated with a fluidized bed. However, reaching the powder level is particularly challenging.

The range of micron sized powder is 1-100um, which can be said to be difficult to embed as the smaller it is, making it very difficult to achieve embedding; For solid dispersions, we can consider it as embedding the molecular morphology API. To unify, we refer to the wrapped material as the core material and the wrapped material as the wall material. For wall materials, some industries also refer to them as protectants, such as freeze-drying protectants and spray drying protectants - this is commonly used in the probiotics industry. Undoubtedly, the products obtained by layer by layer packaging are embedded. If the core material and wall material are mixed and, through some means, the wall material is wrapped around the core material in one step, this is good for production efficiency.

Various industries have made many attempts, which can be divided into wet embedding and dry embedding. Wet method, as the name implies, introduces water or solvent, makes the core material and wall material into solution/suspension/or lotion, and then removes the water and solvent to obtain the desired embedding effect.

First, let's talk about freeze-drying. The formation of a uniform system between the wall and core materials is a prerequisite for achieving ideal "embedding". The reason for using quotation marks is that the freeze-dried material needs to be crushed, and some core components that are difficult to avoid may have particle interfaces exposed after crushing. For spray drying, there may also be core materials on the surface of the sprayed particles (when the grease is embedded, the surface oil will be tested to evaluate the embedding effect).

Freeze drying and spray drying can be considered as obtaining a solid dispersion system, where the core material and wall material are intertwined in a solid state. The wall material indicates that I have done my best to protect you, but I really can't take care of the red apricot that appears on the interface. To achieve embedding, optimization can be carried out through the following approach: secondary embedding.

Before secondary embedding, we need to distinguish between granulation and embedding. The process of granulation is to turn small powders into large particles through a binder. Adhesives are often sprayed onto the surface of powders in the form of atomized droplets, with droplet sizes ranging from 20-50um or larger depending on the atomization mechanism. When the particle size of the powder is much smaller than the size of the droplet, the powder will stick to the surface of the droplet, and the droplet will act as a bridge. After the droplet dries, the powder aggregates into larger particles. When the droplet is much smaller than the particle size, the situation is reversed, which is called coating (embedding). If the particle size of the powder and the droplet is similar, this is also a granulation process. When the particle size of the substrate increases, the subsequent coating is easy to grasp.

Adhesive and embedding materials can be one or more materials to achieve different functions.

Through the granulation process, the core and wall materials in a single particle are in a solid dispersed form; Add another step, wrap more wall materials on the particle surface obtained in the front-end step, and then build a wall next to the wall (widen the wall). To be safe, you can also build a few more walls, and the red apricot will not come out.

When learning about particle coating, most products go through two steps: particle preparation and coating. The fluidized bed one pot method can also be used to achieve granulation and coating, such as the probiotic products mentioned above, which are produced using the one pot method.

Reference: US 11039637

For other industries, typical new energy materials are currently being researched in the field of solid-state batteries. Integrate and connect:

1. Coating modified with solid electrolyte

In order to increase fluidity, stability, etc., due to the small size of the particles, coating materials can also be used to complete bonding granulation and coating;

2. Coating of positive and negative electrode materials

Mix the electrolyte, coating material, and positive and negative electrode material systems, and use the coating material to complete bonding granulation and coating.

At present, the wet coating (or granulation) used in the production of new energy materials industry generally uses spray drying equipment and wet high shear granulation machine, depending on the number of wall materials. When the amount of wall material is relatively large, the suspension is prepared by introducing solvent, and spray drying is relatively appropriate. Considering the type of solvent and the susceptibility of the product to oxidation, a nitrogen environment is necessary. For EHS considerations, the equipment will be designed as a closed-loop system. If there are few wall materials, just like wet granulation in the pharmaceutical industry, the wall materials can be diluted in water or organic solvent, and then mixed and spray added in the high shear granulator to achieve granulation and coating. The reason why fluidized bed is not recommended is that new energy materials are mostly metal or inorganic materials, with a generally high density and fine initial material powder, which is not conducive to fluidization.

After introducing the wet method, let's talk about the dry method. There are many benefits to dry coating, as it does not use water or solvents and has high production efficiency. But it is not suitable for situations where the proportion of coating materials is small.

The dry method in the pharmaceutical industry is generally granulating or coating by heating and melting wax, stearic acid, polymer materials and other materials. According to the characteristics of the coating materials and API, high shear dispersion coating and spray condensation, hot melt extrusion and other means are selected to achieve this. It is still necessary to pay attention to whether there are red apricots coming out (the subsequent crushing process of hot melt extrusion is unavoidable). In addition, there are also many literature on mechanical energy encapsulation.

For the new energy industry, dry coating can be mixed and coated through high shear, or in the form of spray condensation. Sometimes it is not desirable to introduce a bonding medium, and it is desired for the powder wall material to be directly embedded on the surface of another material particle, and to achieve the effect of order mixing and coating. In this case, special equipment is needed to mechanically break down the agglomeration of the wall material powder and coat it on the surface of large particles.

I am currently researching powder granulation/coating. Friends are welcome to come and brainstorm together, and make progress together.