What Causes Hot Melt Adhesive Char

The main causes of char are overheating, contamination, and oxidation. Discover how to avoid them.

Adhesive char is often the main cause of downtime incidents for most end-of-line packaging operations. Once char is formed in a hot melt system, it is almost impossible to remove without extreme measures. Understanding how adhesive char is caused is crucial if you are to avoid it. 

Even after several system flushes, char may still stick to tight corners within the system and continue to cause problems that affect uptime and productivity. Avoiding the formation of adhesive char starts with understanding what causes it.

There are three main causes of char:

  • Overheating
  • Contamination
  • Oxidation

All of these causes will occur on a regular basis in most hot melt packaging applications.

Video: Causes of Adhesive Char


Most hot melt systems use melting tanks to heat the adhesive to the required temperature. The formation of char begins as adhesive breaks down and transforms into gels after long exposure to heat. These gels are unable to flow through a hot melt system and eventually stick to the walls of melting tanks and hoses. Once adhered to the system components, the gels are exposed to excessive heat over an extended period of time and become burnt or charred.

To minimize the formation of char in your end-of-line packaging applications with hot melt system, you must avoid the following practices:

1. Leaving hot melt systems and meting tanks turned on for extended periods of time

2. Increasing system heat settings to compensate for temperature loss or “shocking” when adding room-temperature adhesive to the heated system

3. Using a disproportionate melting tank size for the adhesive throughput


Environmental contaminants such as dirt and dust can create char in your packaging operations. Many manufacturing facilities have a significant amount of contaminants floating in the air as a result of the processes involved. If there is poor ventilation and operators are opening lids on the hot melt systems, particulates can enter the melted adhesive. Once in the hot melt system these contaminants will burn and eventually turn into adhesive char that will stick to system components.

The best approach to avoid adhesive char in end-of-line packaging operations? Prevention! With proper equipment and procedures, you can prevent contaminants entering the hot melt system. 


Adhesive char can also form if melted adhesive is regularly exposed to the air. This can occur if the level control of the adhesive isn’t properly maintained or if the operators are constantly opening and closing the lid on the system. This is a common occurrence as most hot melt systems require manual feeding of adhesive pellets.

By equipping your end-of-line packaging operations with an automatic feed system, you will avoid repetitive lid-opening, thus minimizing oxidation, char formation, unplanned maintenance issues, and costly downtime. 

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