Preventing Stringing in Hot Melt Packaging Adhesives

Best Practices to Reduce Stringing on Production Lines

Packaging plays an important role in food and beverage manufacturing. It protects, extends shelf life and informs consumers about the contents. Brand owners rely on hot melt packaging adhesives to assure a strong seal in their customer products.  To meet the demands of producers, it is critical to keep packaging lines running and minimize downtime while avoiding common issues with the hot melt adhesive application.
One of the most common issues with hot melt adhesive on packaging lines is stringing. When adhesive is applied to the case or carton, it may not cleanly or completely separate from the extrusion nozzle. The adhesive remaining on the applicator nozzle is pulled into a string away from the applied surface. The adhesive string is sometimes called “angel hair.” These thin strands float through the air and can cause many issues on the production line. Some common variables leading to stringing include:

  • Distance between the nozzle and package – closer is better
  • Configuration and nozzle type – single-bead nozzles firing straight down are optimal
  • Size of a nozzle – nozzle size should be considered along with other application specific elements
  • Condition of a nozzle tip – damage or char prevents the valve from operating properly leading to poor cut-off
  • Low solenoid pressure – higher pressure results in better cut-off

In many cases, the adhesive buildup caused by stringing can be fixed by changing operating parameters or the equipment setup. Stringing on a hot melt packaging line can impact operation efficiency by blocking packaging sensors or impacting printing of barcodes and labels.  If the photo eye sensors are blocked, additional cleanup and downtime can result.

Identify Causes of Stringing in Hot Melt Packaging Adhesives

Whether a new or long-time user of hot melt packaging adhesive, there are many factors to consider when troubleshooting issues on the production line.  Problems are generally found in one of three areas: equipment, adhesive or environment.  Any one of these three variables or a combination of them could be the source of the issue. Some common items to consider are:

Equipment: What are the equipment settings – applicator temperature, solenoid pressure, position of the applicator and nozzle shut off? Production line speeds can be changed based on the packaging.  Checking to make sure the equipment settings are optimal for each application is important. If the substrate is too far from the nozzle tip, adhesive can cool down before applying to the case or carton and result in buildup from stringing and other issues.  Additionally, if the temperatures are too low hot melt adhesive viscosity can increase impacting cut-off from the nozzle and increasing stringing or buildup.

Environment: How is the production area set up and is there excessive airflow in the area? Two common problems are air circulation – fans or HVAC – pointed directly at a packaging area and cooler ambient air temperatures in the plant. Both can decrease the drying time of the adhesive and cause stringing.  Check air flow and production area temperatures to make sure there is not too much directed at a specific application point contributing to quicker set times.

Adhesive: How is the adhesive performing – viscosity and temperature? Hot melt packaging adhesive is formulated for different uses.  It is important to consider the recommended applications for hot melt adhesives – like TECHNOMELT.

Understanding these elements on your production line will make troubleshooting stringing issues easier.

Reducing Stringing in Hot Melt Packaging Adhesives

Downtime for manufacturers can be costly. Preventing production issues and keeping manufacturing lines moving is critical for brand owners. Stringing is a common problem impacting consumer packaging. The reduction of hot melt packaging adhesive stringing is achieved by a few easy-to-implement changes to the three variables – equipment, environment and adhesive.


Equipment: settings should be reviewed each time the production lin is changed over

  • Check position, angle, temperature, nozzle size and condition
  • Confirm the nozzle tip is not plugged and in good condition
  • Check the distance from the nozzle to the substrate determine if it can be reduced
  • Check the filters and hoses to confirm there is no buildup or char
  • Check solenoid and tank pressure
Enviroment: ambient temperatures and air flow can shock hot melt adhesive
  • Reduce direct airflow to avoid higher viscosity and premature adhesive drying
  • Audit the air flow in the production area to assure fans and HVAC systems are not directly blowing on application points. This is more critical in applications with higher nozzle to package distances.
  • Plant temperatures are also a factor
Adhesive: specific operating parameters are set by formula
  • Check that the hot melt tank temperature is correct if the hot melt adhesive is too viscous, then the temperature is too low
  • Confirm the applicator temperature is set per the recommended operating guidelines if the applicator and hose are not hot enough, then the adhesive will start to cool while traveling from the tank to the applicator
  • Confirm with adhesive supplier that correct adhesive is being used for the application. Certain adhesives are more prone to stringing than others.

How Stringing Impacts Packaging Production

Reducing stringing from the production line requires understanding the causes – equipment, environment or adhesive – and how to correct them. No matter the application, hot melt packaging adhesives involve understanding how these three variables work together to assure efficient operation and no costly downtime. Adhesive stringing that builds up on equipment, conveyors or packaging is not normal and leads to:

  • Unnecessary downtime affecting efficiency
  • Material waste
  • Poor product appearance

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 a better understanding of hot melt adhesives, register for our digital training platform and learn ways to troubleshoot adhesive stringing to improve production line efficiency.

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