How to Stop Hot Melt Adhesive Stringing

Whether you’re using hot melt for packaging, automotive, print materials, or any other adhesive application, details matter. At best, inefficient use of adhesive can result in waste – at worst, it can cause issues with your system that add to costly downtime.

One of the most common issues encountered with hot melt systems is adhesive stringing. We’ve put together the following guide to help you understand what stringing is, how it happens, and how you can prevent it.

What is Hot Melt Stringing?

Hot melt stringing occurs when some of the adhesive material is left behind on the nozzle and pulled into a string, either automatically down the production line or manually when a handgun is pulled away from the applied surface. The string of adhesive that is left behind is sometimes called “angel hair”.

Hot melt stringing can affect any hot melt application, but it can be problematic for some in particular:

  • In food packaging applications, hot melt stringing can lead to pieces of adhesive breaking off and contaminating food products.
  • In pharmaceutical applications, hot melt stringing can break off inside packaging for medications, which could be mistakenly consumed.
  • In automotive applications, precision adhesive application on visible parts is an important part of ensuring a clean appearance for an automobile.
  • In Case and Carton closing applications , hot melt can appear on the product or case the product is put in.

What Causes Hot Melt Stringing, and How Can I Fix It?

There are various causes of stringing hot melt adhesive, including:

Application Temperature: When adhesive temperature is not high enough, the adhesive can become too viscous and thick, leading to stringing.

Solution: Consult your hot melt Material Data Sheet (MDS) to find the correct temperature settings. Standard hot melt adhesive is typically designed to be set at a temperature of 350° across all zones; however, your MDS may recommend a different temperature based on your adhesive & your application.

Late Shut Off: This is most commonly seen in older AO/SC module configurations, which can shut off slower than newer AO/AC configurations.

Solution: A support specialist at Keystone Industries® is happy to help you determine if the age or configuration of your gun is a factor in your hot melt stringing issues.

Distance from Surface: If the distance between the nozzle and the surface is too great, this can allow air to cool the adhesive after it is applied, leading to stringing.

Solution: Try decreasing the distance between the nozzle and the application surface.

Nozzle Issues: The nozzle’s orifice diameter can contribute to stringing because of its effect on adhesive velocity.

Solution: Try replacing your nozzle. Keystone can help you determine what size could be a better fit for you.

Other potential causes: Over the years, we have seen a variety of different parts and issues contribute to hot melt stringing, including debris build up in hoses and other parts, solenoid issues prohibiting the proper cycling of the hot melt gun, and more.

Keystone is Here to Help

If you’re experiencing hot melt stringing, Keystone Industries® can help you troubleshoot and get to the bottom of the issue. Simply call us at 770-586-5990 or contact us today.

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