How to Prevent Char in Hot Melt Adhesive I
Generally, the best way to overcome the problem of char in hot melt adhesive is to prevent it from ever forming. Once char has formed, however, there is only one way to remove it from a hot-melt system. The entire system needs to be taken apart and the components must be burned out in a burnout oven, completely removing the char. This usually requires replacing seals and recalibrating the hot-melt system as well. It is a time-consuming and very expensive process with no shortcut.
As a matter of fact, hot-melt systems can actually be char-proof, but the key is adhering to the correct procedures required by these systems, as well as developing a thorough understanding of the adhesive. Good communication is your best weapon. Effective and consistent communication between the production and maintenance departments is the best option.
Remember, it is far easier and less costly to prevent char than it is to eliminate it. The only good way to deal with char is to ensure that it never has the chance to infiltrate your system. Following is an explanation of instances where char commonly occurs and how to prevent it.
1. Proper temperature
It is very important to know the details of your adhesive, including its softening point and the temperature vs. viscosity curve. The adhesive manufacturer should provide the maximum temperature for the adhesive, but that does not mean you should heat the adhesive to that temperature. Some manufacturers have a tendency to crank up the temperature to lower the adhesive’s viscosity, but the opposite should be the case, keep the temperature at the lowest possible to still be able to apply the adhesive.
As mentioned earlier, excessive heat breaks down the adhesive formulation, accelerating the gelling and leading to char formation. Some adhesives are much more susceptible to heat breakdown than others, so it is critical that you familiarize yourself with the adhesive and know how prone it is to breakdown. Pot life is the recommended amount of time that a particular adhesive can be under heat in a static state before it starts to break down. Consult your adhesive manufacturer for this information and communicate it to everyone who works with the hot melt adhesive. You might also consider consulting your adhesive manufacturer to be sure you are working with an adhesive that is less susceptible to charring.
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