How to Resolve Hot Melt Adhesive Stringing
Hot melt adhesive users regularly ask what causes their glue guns or nozzles to leak or string. Some refer to the stringing as “angel hair” because of the thin hair-like webbing of adhesive that accumulates on their packaging machinery. This issue can be a simple housekeeping issue or it can be severe enough to cause production downtime. In fact, there are many things that can cause leaking and stringing. Here are the common causes.
If the module on hot melt glue gun is leaking it can easily be identified. With the hot melt system in the ready-to-run mode and while the packaging machinery is idle, simply observe the nozzle tips to see if adhesive is oozing out or dripping while air pressure is on the pump. If oozing is observed, there is a problem with the gun module. Either the ball and seat or needle and seat are worn out or there is an obstruction in the seat area preventing the needle from closing completely. Generally, either by cleaning out the seat area or replacing the gun module can remedy the leaking issue.
However, if the gun module is not leaking and you have stringing or angel hair issues, there are several potential causes. Some remedies are simple adjustments to the hot melt equipment. Most common are incorrect temperature settings. Temperature affects the viscosity or thickness of the adhesive, and the cooler the temperatures the thicker the adhesive, which increases stringing. Standard application temperature hot melt adhesives are designed to be applied at 350° F. It is important that all temperature zones are set to the same temperature. This includes the tank, hoses and guns. Follow the application temperature recommended by the adhesive manufacturer, but generally speaking, the hotter the adhesive the less the stringing.
Another contributing factor to stringing is the distance from the nozzle tip to the carton flap. It’s important to position the nozzle tip as close as possible to the substrate to minimize stringing and angel hair.
If you still have stringing after making these adjustments, contact an expert on adhesives and adhesive equipment, because there may be other system configuration issues contributing to the stringing, including the distance from the air solenoid to the glue gun and nozzle orifice diameter or engagement length. There are also newer glue gun technologies that utilize air-open and air-close designs as opposed to the older air-open, spring-close technologies. Air-open / air-close guns shut off faster thereby minimizing stringing. Some companies offer zero-cavity module designs that eliminate stringing.
Lastly, it could be that your adhesive technology is outdated. There are newer metallocene-based hot melt adhesives that do not string, char or smoke and they could be a good option for your packaging operations.
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