PUR itself has undergone a multitude of developments and improvements over its thus far short lived presence in the binding industry;

The first generation PUR raised concern amongst books manufacturers, since it had to sit for nearly 24 hours after binding before it had cured sufficiently to have developed enough strength to withstand the shipping process.

Second generation improved upon its predecessor, and built this level of strength after just four hours of binding. However a certain level of moisture was required in the paper during this time, and in the winter months the relative humidity in binding plants in some areas dropped to an insufficiently low level.

Again improving on second generation PUR, the third generation required only the moisture present in the paper to cure properly.

By the advent of the fourth generation, cost-effective improvements to the adhesive had been implemented, improving the pot life before application and allowing plants more time for use before a new batch was required.

In just a short space of time- twenty years or so, you can begin to see how modern chemical understanding is allowing us to produce better and better adhesives, one after another.

Given that the first two major leaps in perfect binding technology lasted for around fifty years each before being replaced, think about how much more we could be able to do with PUR-based adhesives in the next fifty!

This was the fourth and final part in a short series detailing the evolution of traditional bookbinding up to the modern day and a short insight into developments made in the field of perfect binding.

From the Purely DIgital team, we hope you found the series interesting and informative!

The Introduction of Polyurethane Reactive (PUR) in Printing

Moving towards the present day, advances in perfect binding came one after another and once more towards the end of the 1980’s, technologies in bookbinding took another dramatic leap upwards with the advent of PUR.

PUR is the shorthand name for the more recently introduced binding option polyurethane reactive.

Polyurethane reactive is unique in that it will bond to many types of coatings and films as well as paper and superior to other hot-melt adhesives with its ability to allow a book to lie flat whilst open- the benefits of which shall be discussed in a little further detail later on.

The latest PUR adhesives as modern binding mediums are highly versatile, with the changes in paper weight and inks along with the various coatings used by today’s printing industry posing it little challenge. Additionally, with traditional adhesives when the migration of inks into a book’s gutter can bring about binding issues, PUR adhesives are said to remain virtually unaffected.

When applied at its recommended thickness – ~0.01 inches, polyurethane reactive is considerably more flexible than standard ethylene vinyl acetate hot-melts. This characteristic allows PUR-perfect bound books to lie flat on their own whilst open, a useful trait which enables hands free reading.

An example of the benefit of this is in user guide/manual manufacture; have you ever tried holding the instructions for a new piece of kit open whilst trying to configure your new toy? Not an easy task, if I might say so myself- and now a task which is no longer necessary. Thanks to this attribute, according to National Adhesives, both the world’s largest software seller and a Texas based computer manufacturer chose PUR for all their instruction manuals several years ago.

This is the third and penultimate part in a short series detailing the evolution of traditional bookbinding up to the modern day and a short insight into developments made in the field of perfect binding. Check back a week today for the final part in this series, an overview in the many developments and improvements in PUR.

The Advent and Development of Perfect Binding

The first early attempts at perfect binding employed traditional, flexible animal jelly glues, however attempts at perfect binding only really became commercially viable with the development of synthetic resin dispersion technologies using water to help allow the adhesives seep into the paper’s pores at the site of adhesion.

In the first perfecting binding techniques of this type, the adhesive solution used typically consisted of 40-50% water which would require evaporating away as part of the curing process.

Adequate drying facilities had to be incorporated into the in-line drying facilities thanks to this, meaning that the equipment had to be large and therefore expensive.

One such method for drying books to which the adhesive had been applied was via high frequency drying, where hot air was passed through an oven through which the books would pass through, heating and evaporating away unwanted moisture and curing the adhesive.

Using cold glues in techniques derived from the above led to books with the tendency to become brittle over time or with frequent use. Nearly 50 years after the advent of the first perfect binding methods and commercial viability of automated bookbinding, the process was developed further with the DuPont Company introducing a hot-melt binding process c.1940.

The advent of hot-melt adhesives provided several advantages to the manufacturing side of book crafting; volatile organic compounds which can pose health risks to those exposed to them are either greatly reduced or eliminated and the adhesive curing step is also eliminated.

The fact that there is no curing step involved with hot-melt adhesives leads to a greatly reduced setting time, which in manufacturing terms means much less space is required to store the unfinished products and the turnaround time for a product batch is also slashed

The introduction of hot-melt adhesive in bookbinding allowed for the first time high-speed in-line finishing and trimming on larger binding systems and brought feasibility to the development of smaller scale binding machines, allowing the production of smaller, cheaper binding machines with a lesser output.

The production of books in this manner saw the advent of the phenomenon we see now as an everyday thing; the widespread production and uptake of the paperback book. The original pioneers of the paperback book, Pocket Books is now a division of Simon & Schuster, a successful publishing company now in the top 6 of all US publishers.

This is the second part in a short series detailing the evolution of traditional bookbinding up to the modern day and a short insight into developments made in the field of perfect binding.