| Cline's Comments |
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| Page Pull Development |
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| Page pull development has always been a major concern of binders. With standard EVA adhesives, page pull occurs within minutes and builds slightly over the next hour as the polymer orients. With the first generation PUR, page pull development took as long as 24 hours. The second generation PUR reduced this time to four hours, and the current PUR develops meaningful page pulls after 30 minutes. But the real question is, "What will my final page pull values be?" Whether books are bound with PUR or with EVA, the most important consideration is the roughing of the backbone of the book. This factor is discussed in this issue's lead article. I would like to address the other two factors that influence the other 5-10% of the ultimate page pull values. |
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| Hot Melt Composition |
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| The first factor is the composition of the hot melt. Hot melts are generally a combination of polymer, resin and wax. By choosing various combinations, the formulator can produce a hot melt with different properties. If adhesion is the primary concern, more expensive resins and waxes can be used. If cost is the major concern, the formulator might select lower quality resins. The tackifying resin is generally considered the most important component of the hot melt that contributes to adhesion. The correct wax will influence the trimmability of the book. The choice of polymer is rather limited, as this provides the backbone of the hot melt, and requires high molecular weight to provide tensile strength and toughness. |
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| Viscosity |
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| The second factor influencing page pull values is the product's viscosity. Since the hot melt is mechanically pushed into the backbone of the book, high viscosity products are at a disadvantage. This is especially true for highly filled or gloss coated papers where it is difficult to expose fibers to which the adhesive will attach. But neither do very low viscosity products perform well, especially on high speed binders, because the applicator wheels spin so fast that it is difficult to keep sufficient adhesive on the wheels. Gaps and/or voids in the glue occur on the backbone. As one can see, choosing a hot melt in bookbinding is not as simple as asking for a "five second glue." Many factors need to be weighed before selecting the proper adhesive. Your National sales representative is ready, willing and able to provide you with the proper product for your application. |
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Chuck Cline |
| Technical Service Manager - Bookbinding |
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