When manufacturers have to deal with coke, valuable production time is wasted. Therefore, it is important to understand the causes of EVA hot melt adhesive carbonization and how to prevent it as much as possible.
The hot melt is carbonized in a water tank, and the char is composed of burning particles resulting from the thermal degradation of organic matter. This can include:
certain adhesives
paper material
plastic
polymer
other pollutants
How Hot Melt Adhesive Causes Carbonization
Charring can be a common problem with hot melt adhesives used in packaging applications. These applications often require placing the adhesive in a large melt tank. This means that the adhesive is stuck in the can and “cooked”. Over time, some EVA hotmelts may char slower than others, but all types of hotmelts may be susceptible to this problem over time.
How Preheat Tanks Cause Charring
If not maintained properly, the reservoir can cause charring and damage to the entire unit. This can happen if the melt tank lid is left open for too long and contaminants fall into it.
Additionally, the reservoir may not be the right size for a given application and line throughput. This affects how much adhesive is used and how much adhesive is left in the tank. Also, if the sump temperature is too high, it increases the likelihood that the adhesive will “cook” faster and cause charring.
Solutions to reduce carbonization of hot melt adhesives
The EVA hotmelt used is the right one for your application. In some cases, low application temperature binders or metallocenes can do the job and are less prone to charring. However, some adhesives char more easily than others but are still suitable for specific applications. The sheet or process may require a binder that is easier to char to achieve the desired properties.
Tips for proper maintenance of the preheat tank include:
1. Always maintain the adhesive level in the container at 70% or more of the container capacity.
2. If the binder level is too low and cold binder is added to fill the tank, the overall temperature of the binder will drop and may result in higher viscosity and stringiness.
3. Another reason to keep the preheat tank full is the formation of char in the presence of high temperature and oxygen. If the adhesive level in the tank is allowed to get low, adhesive residue adhering to the sides of the melter can be exposed to the air and heat up on the sides of the melter. These are perfect conditions for char formation.
4. Make sure that the size of the preheat tank is suitable for the amount of glue applied to the production line. The goal is to have the binder turned at least once a day so that fresh material can be added regularly. In most applications, a smaller melt bath is considered better because it reduces the time the adhesive stays in it.
5. Keep everything around the hot melt can clean and take good care of the lid.
