The Glue Talk Blog

Boxes at the end of a line representing case and carton sealing.

Adhesives 101: Case and Carton Sealing

Posted 02 Apr 2019 by Randy Slezewski, Senior Application Specialist

Nearly every case and carton adhesive application in converting involves the use of a hot melt adhesive to seal the flaps. The adhesive is applied at an elevated temperature to one flap, which is then placed in contact with the surface of the secondary flap. These are then compressed to form a bond that seals the case or carton.
Naturally, your production crew is striving to get optimal performance from these hot melt adhesives—but doing so requires a basic understanding of the many factors that can impact the performance of the hot melt. These include substrate, substrate temperature, application temperature, application amount, compression time, and open time. In addition to these common variables, there are other factors that can also affect the performance of your hot melt, including:

  • Changes in ambient conditions, even for a short time. For example, opening a nearby dock door in a cold environment or using a fan in hot conditions.
  • The use of substrates that were stored in unheated warehouses and weren’t brought to room temperature prior to use.
  • Applying more adhesive in search of better bonds. Too much adhesive can actually slow down the set time and create cases that open right out of compression.
  • A switch to a new supplier of cases or cartons.

Also, because the typical hot melt used in converting is thermoplastic, it is susceptible to softening under higher temperatures. Your hot melt selection should be driven not only by the parameters of the converting line but the environment the sealed case or carton will see during shipping.

One more thing to keep in mind is that the listed melt temperature or softening point of an adhesive is not an indication of its heat resistance performance. For example, a hot melt may soften at 221°F, while its heat resistance is only good for 150-160°F.

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