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What is Char in Hot Melt Adhesive


If you are involving with hot melt adhesive or other related products, you may realize that there is no greater villain in a hot-melt operation than char. While char terrorizes many hot-melt operations worldwide, you actually have the ability to eliminate char and char-related problems. Before we can delve into how to defeat this malicious adversary, let’s make sure you understand your enemy.

First of all, let’s figure out what is char. Generally speaking, char is adhesive that has been blackened or burned. It is a particular challenge to hot-melt operations because of the heating and melting process required. Usually, char can result from heating the hot melt adhesive at a too-high temperature, exposing the hot melt adhesive to heat for too long, or exposing the hot melt to heat and oxygen.

When the effects of heat, time and oxidation begin to attack the hot melt, the adhesive starts to break down, as the adhesive’s polymer chains begin to form active sites. These sites can then combine to form gels. Gels stick to the walls of hoses and crevices in melt tanks, forming an anchor. Anchored hot melt does not effectively flow through hoses and tanks. Instead, these anchored pieces of hot melt are exposed to too much heat and begin to form char, or burnt adhesive. In almost all cases, the blackened char wreaks havoc on the coating and laminating process.

It is important to note that char is a tricky enemy, which does not always come from adhesive. In some cases, char is actually burnt particulate that gets into the adhesive. This is almost always the result of poor housekeeping. If the lid of the melter or adhesive container is left open, the contents are exposed to particulates, thus inviting char into your operation.

Once formed, char bakes onto the heated grids. And once this happens, it breaks off in pieces and clogs filters, stops up spray nozzles, clogs bead nozzles, works its way onto the substrate, leaving marks, streaks and uneven surfaces, and eventually works its way into pumps, breaking seals, and scoring and damaging the pump walls.

One of the most problematic issues with char is that once it gets into your systems, it is impossible simply to flush out. There will always be dead areas (corners) that can’t be flushed. The char hardens on the surface and continues to collect in those places. Those ever-growing char spots periodically break off and cause ongoing problems. Basically, once you get a char problem, it causes ongoing product quality problems, extensive maintenance issues, and work stoppages. You will be fighting a never-ending battle until you take extreme measures.