P.U.R. Glue: Perfect Binding Made Perfect

Lap Glue is generic P.U.R. Glue (Polyurethane Resin) is the latest and greatest problem solverin perfect binding. 

Lap Glue is a generic term to describe hotmelt or cold glue which is applied in the perfect binding process inside the front and back cover, near the spine, to produce a hinge effect on the covers.










Perfect bound books that fall apart after little use are becoming a growing and perplexing problem in the bindery world.

To learn more about this phenomenon I talked to nine major trade binderies and chemist Chuck Klein of Nacan Products. These people have run into this very problem and are familiar with the cause.

Usually, the cause of this problem is ink solvent migration. What frequently happens is the finished books are tested and meet all of the bindery guidelines such as pull tests, flex tests, and subway tests. Two to four weeks later, horror of horrors, the books start falling apart after only minimal use.

Hotmelt adhesives have not changed a great deal according to Bill Crowe of Nacan Products. However, as the ink composition and paper composition have gradually changed, printers are faced increasingly with the problem of ink solvent migration.

In the past, ink solvent migration had not been a problem because sheetfed presses traditionally ran at slower speeds and required conventional inks. Today’s high-speed sheetfed presses require inks which are formulated for faster drying. These inks simply oxidize on the paper’s surface rather than dry. Last year, at a Binding Industries of America seminar held in Florida, Chuck Klein from Nacan stated that tests have revealed that as much as half of the printing solvents used have not dried after two months.

There is also a problem using coated papers. Coated papers have increasingly more coats, and as long as coats are less expensive than paper fiber we expect that we will continue to see an increased amount of “filler” in the manufacturing of paper.

Fundamentally, no problem exists with inks which are used on heatset web offset presses. In this context, solvents in the ink evaporate in the drying process. In sheetfed printing, stronger chemicals are used to allow for quick-setting. The stronger solvents used in the inks on sheetfed presses have numerous benefits for the printing process but, for all intents and purposes, the vast majority of hotmelts used for perfect bound books degenerate and breakdown, when “attacked” by these stronger solvents.

The two best solutions are:
1. Printing the job with no solid ink into the gutter.

2. Specifying that if the job necessitates solid glue into the gutter, ensure that the perfect bound book is bound with P.U.R. (polyurethane resin) hotmelt glue. Using standard hotmelt glues on a sheetfed job, using solvent inks, and printing with solid ink into the gutter can be a prescription for disaster.

Let us use our new P.U.R. Glue system for your next perfect binding job!