Better Finishing Through Chemistry
There are some of us who are old enough to remember the Monsanto commercial, and its famous “better living through chemistry” slogan. I was reminded of this during a recent finishing project. We had been having issues with a cold-glue application system on a complex finishing line. The application nozzle was meant to apply a programmed series of micro dots to a portion of a sheet, but the application gun had issues.
When a very experienced tech from the systems manufacturer showed up to help, he immediately noted that the ambient temperature in this portion of the plant was kept pretty cool; 66° F. in fact. Not your average working temperature. This was causing the cold adhesive to thicken and the gun to drop globs of glue on the sheet instead of nice neat dots. The cure? A cold glue with a different viscosity which was better suited to this temperature.
Adhesives are widely used in finishing, this includes perfect binding, folding, mailing, and folding carton applications. And coatings and various chemical solutions are used in the digital print process to both enhance image quality and make the paper more “finishing-friendly.” Both chemistry and environmental control have a lot to do with systems performance.
In perfect binding, accurate temperature control of binding adhesives—whether hot or cold—will affect their application and penetration into the substrate, as well as their bond quality with the paper. Adhesive viscosity and quality can change dramatically with swings in application temperature. In effect, the chemistry of the adhesive is subject to the controls of the storage and application systems. Hot melt adhesives need clean and temperature-controlled melting tanks. Cold adhesives (and some hot adhesives) need sealed tanks with little or no outside air penetration.
Adhesive systems need regular cleaning and calibrating to perform at their best. Likewise, digital papers will commonly be treated with a variety of chemicals not only to enhance print quality, but to affect finishing. A silicon and water mixture is often applied to a digitally-printed web just before it enters the inline perfect binder or saddlestitcher. The main effect is to reduce static charge in the paper caused by both high heat and moisture loss during the print cycle.