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The Problem of Char: Common Causes

Ethylene vinyl acetate (EVA) adhesive is widely used for packaging hot melt applications. However, because of its chemical composition, EVA tends to develop carbon buildup, or char, inside of adhesive application tanks, lines, hoses, and nozzles.

Char — carbon buildup — occurs when EVA oxidizes at prolonged high temperatures above 350º. This heat and oxidation reaction creates carbon buildup during idle periods when adhesive is not flowing through the system, due to degradation of the EVA.

During packaging operations, Char Clogs Applicatorsince adhesive which flows closer to the walls of a hot melt applicator hose moves more slowly than the adhesive flowing in the center of the hose, adhesive nearer to the outer wall of the hose wall tends to degrade more readily, becoming thicker and sticking to the inner walls of the hoses, and eventually forming char on the inside of the hoses, adhesive tank, and nozzles of your hot melt adhesive application system.

 

Next Time: What happens when char is present.

(Excerpted from “No More Char”, a recent issue of Evans Adhesive Solution Advisor. Download entire issue here.)

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