| Cline's Comments |
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| What's the Best Glue for Backlining? |
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| Backlining is an integral part of making a quality book. The backlining process consists of rounding the spine of a glued-off book and bonding crash and kraft paper to it. (The kraft paper may or may not have headbands bonded to it.) The crash, or super, is a mesh material that has very high tear resistance. The kraft paper is a simple 80-pound or greater brown paper which may or may not be made flexible by impregnating it with a rubber. |
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| Animal glues have functioned mostly for this process in the past. While animal glues possessed the high tack and long open time necessary for bonding the crash and kraft, they often were very brittle, causing the book to crack when opened. This cracking eventually would lead to a loss of adhesion as the animal glue turned to powder. |
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| The trend has moved toward replacing these animal glues with hot melts and retrofitting the existing systems. Many of the new lining machines come equipped with hot melt applicators. |
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| Which Hot Melt? |
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| The type of hot melt to use for backlining has been a subject of many discussions. Since most backlining systems apply the hot melt in a thin film with a wheel, the hot melt needs a long open time. Many book binders feel that long open time EVA hot melts should be used, while others perfer pressure sensitive or semi-pressure sensitive hot melts. |
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| Some binders favor long open time EVA products because they clean up easier than pressure sensitive types. This is true. But the key is to keep the hot melt from getting all over the machine - which is easier said than done. You can take steps, however, to minimize the effects of pressure sensitive products, such as coating the exposed parts of the lining machine with a non-stick material. |
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| Many binders believe the EVA products resist heat better than pressure sensitive products. But in fact, the heat resistance of National's 34-1211 or 70-007A pressure sensitive adhesives is greater than that of most EVA lining glues. In order to increase the open time of EVA products, the softening points of the raw materials must be lowered, which lowers heat resistance. |
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| Wide Operating Window |
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| Pressure sensitive products, due to their nature, have a much wider window for operation. The lining machine can be shut down for lunch with books in every station, and when started up, every book will be bonded as strongly as if it had been sent through directly. Even though EVA products have higher tensile strength, the pressure sensitive products produce stronger bonds because when stretched, they dissipate the stress throughout the entire bond. |
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| As mentioned, some papers used for lining contain additives that are difficult to adhere. The pressure sensitive products do an excellent job of bonding these surfaces. |
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| Headbands can also be a source of adhesion problems. Many headbands contain starch as a sizing compound. Here, the pressure sensitive products will wet out the surface and bond to the cloth fibers better than EVA products. |
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| In conclusion, each bindery must weigh the advantages and disadvantages of using a particular type of adhesive for lining. The staff must decide whether the easier cleanup of EVA or the wider window for application and adhesion of pressure sensitives is most important. |
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Chuck Cline |
| Technical Service Manager - Bookbinding |
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