WHY YOU SHOULD NOT MIX HOT MELT ADHESIVES
Imagine filling your car with diesel instead of gasoline. Or gasoline instead of diesel. That wouldn’t be good. You wouldn't drive far – if anywhere – and the engine would definitely suffer damage. The situation is similar with hot melt adhesives: Mixing adhesives will damage the adhesive application system sooner or later and this will result in downtimes due to charring or faulty adhesive application.
Take the same approach as with a car: Don’t mix what doesn't belong together
Every adhesive has specific properties. Even if the hot melts look the same, that doesn’t mean they have the same chemical structure. Suppose you replace an adhesive with a processing temperature of 150–170°C with an adhesive that is processed at 130–150°C. If you add the new adhesive to the old one in the tank, two things will happen: Firstly, the new adhesive will burn because the temperature in the tank is too high for it. Secondly, the viscosity of the adhesive decreases when it is heated above its processing temperature – it becomes very thin. The thin adhesive is transported through the system more quickly because it flows better, while the old, thicker adhesive remains in the tank and burns. Burnt glue is not immediately noticeable, but once charring has set in, it can settle anywhere in the adhesive application system – with disastrous consequences, as heated hoses can become obstructed, and application heads can become clogged.
Every adhesive has specific properties
What you will notice right away, though, is a faulty application. If, for example, the viscosity is too high due to incorrect temperature settings, the adhesive will be too thick – and too little adhesive will be applied. If the viscosity is too low, on the other hand, too much adhesive will be applied because it is too thin. However, faulty adhesion also occurs when the open time – i.e. the time in which the adhesive sets – is too long or too short. None of this has to be the case. Just follow the simple rule: Never mix different hot melt adhesives!
Clean adhesive is needed for a clean adhesive application
CLEAN THE ADHESIVE APPLICATION SYSTEM EVERY TIME YOU CHANGE THE ADHESIVE
You can, of course, replace the hot melt adhesive in your adhesive application system. Maybe you want to glue a new product or the old adhesive is no longer available. Whatever the case may be, it is important that you clean the entire adhesive application system thoroughly so that the old and the new adhesives do not mix. It’s worth investing three to four hours to do so. Downtimes due to burnt adhesive and clogged application heads or hoses cannot be planned for, troubleshooting is difficult, and the required cleaning takes much longer: In the worst case, you will no longer able to avoid replacing hoses or application heads. Therefore, create the best conditions for the new adhesive with thorough cleaning right from the start.
A cleaned adhesive application system is the ideal basis for a successful adhesive changeover.
WAS THE EFFORT WORTH IT?
What are your experiences? I think that if you are interested in high-quality gluing and want to produce without unplanned interruptions, then the effort is definitely worth it! If you also maintain and clean your system regularly, the effort involved in any adhesive exchange is reduced.