Are Protein-Based Adhesives Ready for Bookbinding?
We have seen lots of advances in adhesives for bookbinding over the years, with PUR (polyurethane reactive) adhesive being the last major game changer. PUR was a godsend to printers and binders struggling with the challenges created by digitally-printed substrates containing silicone-based fusing oils and other chemicals. But PUR came with its own limitations, tight tolerances on application amount, and up to 24 hours of cure time to reach full strength.
EVA hot melt has always been the standard prior to PUR, and still dominates in bookbinding. EVA cures almost instantly by rapidly cooling from a liquid to a solid. PUR cures by reacting with moisture in the atmosphere, a much slower process. But there is now revived interest in protein-based adhesives. Protein adhesives - or “animal-based” polymer glue - is formed through the hydrolysis of the collagen from skins, bones, tendons, and other tissues similar to gelatin.
They have been widely used in casemaking for hardcover books, but they also have distinct advantages in conventional bookbinding. They can be applied at much lower temperatures than standard EVA hot melts. Typically, 140° - 150°, versus 270° - 350° for EVA. This reduces energy consumption and is easier on the gluepot, plus greatly reducing the potential for operator burns. Secondly, they are much more resistant to heat, and to “cold cracking.” Then there is the biodegradability issue. Protein glues are biodegradable, while PUR is not. And to top it off, protein glues are cheaper per pound than PUR adhesives, and have better “lay-open” properties for books.
But there some roadblocks. Protein-based glues fare poorly with coated substrates, and have a longer cure time than EVA hotmelt. They’re also not easy to extrude. But they’re used in lots of industries, including packaging, where their green properties, greater safety, and lower energy costs are well-received. One of the advocates of this technology is Bio-Bond LLC of Peosta, Iowa, which markets its protein glue under the trade name Cooler-Melt. Bio-Bond has only been around for a few years, but has had inputs and guidance from veterans of the high-volume bindery segment. It will be interesting to see if it can convince bookbinders and equipment manufacturers that it has a better mousetrap. My thanks to Gary Arnold for his assistance on this blog.