Preventing Hot Melt Adhesive Char

Troubleshooting Causes of Char in Hot Melt Packaging Applications

From sealing a box of pasta to securing a label on an energy drink, hot melt adhesive is one of the most versatile products in packaging operations. It enables manufacturers to package the products consumers use daily efficiently and safely. Hot melt packaging adhesives are designed to set quickly under short compression times to form a strong bond. To meet consumer demand, packaging lines need to run smoothly and avoid downtime. One of the culprits reducing the efficiency of a packaging operation is char – it can impact the hot melt equipment and increase downtime. Once char is in the system, removing it can be difficult.
Char results from heat, contaminants and oxidation of hot melt adhesive. As the polymer chains begin to breakdown, the over-exposed adhesive begins to burn – or blacken – and clog the filters, hoses or nozzles on the hot melt equipment. Char can wreak havoc on the dispensing and sealing of consumer goods packaging. The cause of char is difficult to diagnose, and the sources can be a combination of equipment settings, operating processes and adhesives. The conditions which make the hot melt system more susceptible to the formation of char are:
  •  Operating equipment above recommended temperatures for hot-melt adhesive
  •  Overexposing hot melt adhesive to high heat for long periods of time
  •  Extending exposure of hot melt adhesives to oxygen and contaminants
These conditions can be easily remedied by implementing some best practices on the hot melt packaging line.

Optimizing Hot Melt Packaging Adhesive Performance

Hot melt adhesives char can cause ongoing maintenance issues and product quality issues resulting in downtime on the production line. Once char infiltrates a system, it is difficult to completely flush out. Dead areas, such as bends and corners of tanks, will always exist and cannot be easily cleaned. Hardened char can continue to collect in these places and will break off causing clogs to filters, hoses and nozzles.
Prevention by establishing standard operating procedures is the easiest solution. A combination of understanding the optimal performance for the equipment and adhesive is critical. Some other best practices to implement, include:
  1.  Avoid running above recommended operating temperatures – the elevated temperatures. promote adhesive degradation at higher rates and increase the formation of char.
  2.  Prevent overfilling the hot melt adhesive tank – if adhesive contacts the lid or builds up around the rim of the tank, it will not circulate, and it will stay in place and cook forming char. This can also potentially prevent the lid from closing all the way until the glue melts and gets used.  This allows dust and other contaminants to enter the tank, potentially leading to more char formation
  3.  Maintain consistent hot melt tank filling to prevent underfilling – residual hot melt adhesive clinging to the tank walls will burn if filled below the recommended line. Tank filling is a critical element in preventing char formation.

  4.  Keep hot melt adhesive supply covered (box/bin lid secured) – dust, corrugate fibers or other contaminants can impact the adhesive chemistry. Protect the hot melt adhesive supply while in storage and in the tank. Keeping the lid closed and free of debris is an important element in avoiding dust and contaminants.
  5.  Avoid build-up on the mesh inlet – this filter between the adhesive supply and the pump drain can be a build-up location for hot melt adhesive and cause dead spots. Clean debris from the mesh inlet frequently.
  6.  Prevent moisture intrusion – when moisture enters the hot melt adhesive equipment, the oxygen burns and leads to bubbling or char within the system. The moisture can also impact the effectiveness of the adhesive bond and lead to pop opens.
Once char has formed, operators will battle this problem until extreme measures are undertaken. There is a single way to completely remove char from a hot melt packaging production line, and it involves shutting down the entire system. The hot melt system needs to be disassembled with the components run through a burnout oven to remove the char. Costly and time consuming, it will also require replacing various parts and recalibrating the equipment. Prevention can keep the hot melt packaging line running smoothly for an extended length of time. There are also ways to try and flush the system; however, any approach should involve consulting the equipment manufacturer guidelines.

Maintaining Hot Melt Equipment to Reduce Downtime

Hot melt adhesives and equipment became mainstream in the packaging industry in the 1960s. They are considered the standard for case and carton sealing, labeling and pallet stabilization. Ease of use and functionality make hot melt systems ideal for bonding all types of substrates. Each hot melt adhesive system is designed to fit different operating needs based on the application and equipment manufacturer. As these needs change, the equipment should be adjusted to avoid issues which can cause char formation.
Monitoring the equipment performance is an important part of optimizing the packaging line. How the system and the adhesive work together is critical. Some equipment best practices, include:
  1.  Utilize setback mode – this equipment feature allows the adhesive to cool down. Leaving the hot melt equipment at full temperature when not running for extended periods of time, can cause char. Establishing a setback or standby mode routine extends the adhesive’s pot life
  2.  Avoid leaving the tank lid open – tank maintenance is important to avoid contaminants or debris entering the tank. The tank lid should be properly sealed every time after it is opened for filling. Broken or ajar lids risk molten hot melt adhesive clinging to the rims and causing further issues. Keep everything clean around the hot melt tank and maintain the lid properly.
  3.  Prevent crimping or bending of hoses – dead spots or hot spots can form in bent hoses. It is important to avoid tie wrapping the hoses to prevent the adhesive from sticking to a specific area and forming char.
  4.  Follow a preventative maintenance plan – adhering to a recommended maintenance plan of cleaning and replacing parts as recommended by the hot melt equipment manufacturer will increase the useful life of the equipment.

Best Practices to Reduce Char in Hot Melt Adhesive Systems

Understanding how to maintain operating consistency with hot melt packaging adhesive is important. Each equipment manufacturer has best practices to keep the machinery working efficiently and effectively. Along with proper operation, assuring the equipment is sized appropriately for the production capacity aids in avoiding char formation. The effects of char can include:
  •  Clogging filters and nozzles causing downtime and incurring maintenance costs
  •  Impacting the adhesive line as char works its way onto the substrate, leaving marks, streaks and uneven surfaces
  •  Damaging pumps, breaking seals and scoring pump walls
Food and beverage manufacturers rely on the effectiveness of hot melt packaging adhesives to assure a strong seal or bond. Brand owners need to understand the optimum adhesive performance to produce a secure bond. To gain more insights on ways to increase efficiency of hot melt adhesive, register for Henkel’s digital training platform and learn more best practices about improving the operating life of adhesive.

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