| Tech Tip |
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| Avoid Hot Melt Char Buildup |
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| In edition binding, the backlining station applies the crash, kraft paper and headbands. Many of the old animal glue pots are being converted for hot melt adhesives, and some of the newer models have hot melt applicators as standard equipment. |
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| Char buildup in the hot melt application pot can cause serious problems in book quality. Char occurs when excessive heat raises the temperature of an organic material such as a hot melt. This heat causes the polymer to break down into small chain lengths, and eventually into carbon. The carbon material sticks to the side of the pot, and eventually breaks off in visible chunks, which we refer to as "char buildup." |
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| In the early stages of char buildup, the hot melt darkens. This is due to the dispersal of the carbon throughout the molten material. All hot melts will form char eventually, but the use of antioxidants will prolong the life of the product. Once this char has built up on the sides and bottom of the pots, the flow of the hot melt breaks off the char. Since there are no filters in the pot, these small chunks flow in the pot until they lodge in a corner or under a scraper. |
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| When the char particles accumulate under the scraper, they cause erratic application of the hot melt to the backbone of the book. This makes it appear that the hot melt is setting too fast, when in fact little or no hot melt is being applied to the book. |
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| As one remedy, use a thin nylon or teflon scraper to keep the space between the wheel and the edge of the pot free of char. However, since there are no filters, this char will eventually return to the scraper and cause problems again. The real answer is to maintain and clean these pots on a regular basis and to work with a hot melt that has superior heat stability. |
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| Lining units that have been retrofitted with extrusion systems will not experience char buildup, as in-line filters prior to the application of the hot melt remove any foreign material. |
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