July 06, 2021
Years ago, Friesens used PUR (Polyurethane reactive glue) to bind their softcover books when requested. The result at the time was not significantly better than the regular hot melt glue we also used. It was costlier, so we went away from using it. Over time, suppliers improved PUR glue significantly making it a user-friendly and more reliable product to work with,
Our new Muller Martini Bolero Perfect Binder has the option to use a regular hot melt glue or PUR glue. When we run coated stock jobs on our perfect binder with our regular hot melt glue, we can run into difficulties whereby the glue does not flow nicely into the sections and contact all the pages of the book. If we cannot get the glue to contact all the pages, the pages can fall out of the book more easily. Therefore, at times we have had to grind the spine down slightly to allow better flow of the glue to each page of the book. If we grind too much, and the pages of the book become single sheets, the hot melt glue is not aggressive enough to bite and hold the sheets of coated stock and create a high quality bond. In some instances, that makes it easier for the single page sheets. It is a constant battle between grinding too much and getting glue to contact each page.
Using PUR glue is a great solution to the problem surrounding the perfect binding of coated stock books. Here are some qualities and details that PUR glue offers:
- PUR glue is an aggressive glue that bites nicely into all types of materials, especially coated stocks.
- PUR glue is very flexible when applying a thin layer (if you apply too thick of a layer it becomes rigid).
- PUR glue requires us to grind the sections to single pages and allows us to apply the thinnest layer of glue possible and ensure the glue touches every page of the book.
- PUR glue takes longer to cure than hot melts. It uses the moisture in the air for curing and takes twenty-four hours to fully cure when a thin layer is used. We cannot use PUR glue for notch-bound books, as the PUR glue layer would be too thick and the glue may not fully cure. It also would create a very stiff book.
In the past we recommended a coated stock job be sewn instead of perfect bound for the most flexibility and strength. While we still believe sewing is the strongest and the most flexible method, we also believe PUR glue binding to be a close second and gives our customers a quality product.