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Custom Book Printing: What is PUR Binding?

A Perfect Bound book made with PUR adhesive

PUR Binding

PUR Binding is a popular bookbinding method that uses a high-performance bonding agent known as Polyurethane Reactive adhesive (abbreviated as PUR).

PUR Binding is a type of Perfect Binding. Perfect binding involves applying a strong adhesive to the spinal edge of a book's page block and then affixing a wrap-around cardstock cover over the page block. The adhesive bonds the cover and pages together at the spine. After the adhesive cures, the three open sides of the book are trimmed to give them clean "perfect" edges.

The Evolution of Adhesives used for Perfect Binding

Though the Perfect Binding method was invented in 1895, it wasn't widely used until paperback books started being mass produced in the early 1930's. However, these early books used a basic "cold" glue that became brittle with age.

In 1940, Dupont introduced a hot-melt adhesive that offered better flexibility. Known as Ethylene Vinyl Acetate (abbreviated as EVA), this glue still has widespread use today and is considered the traditional perfect binding adhesive.

Unfortunately, EVA glue developed its own share of shortcomings. For example, it can crack under certain circumstances and often fails to perform in extreme temperatures. Fortunately for the bookbinding industry (and many other industries), Polyurethane Reactive adhesive (PUR) was developed in the 1980's and has been growing in popularity ever since.

What does Polyurethane Reactive mean?

The term "Polyurethane" refers to a string of polymers linked together by urethane bonds, whereas "Reactive" means that the adhesive gains its strength from a chemical reaction.

In the case of PUR, this chemical reaction is triggered from moisture that naturally exists in the surrounding air and the material being glued.

The PUR formulation combines the rapid bonding speed of a hot melt adhesive with the enduring strength of a structural adhesive.

How Is PUR superior to EVA?

Though EVA and PUR are both hot-melt adhesives, PUR is vastly superior to EVA in many ways…

Stronger Bond -

Unlike EVA glue, PUR will adhere tightly to a wide range of materials, including heavy cardstocks, synthetic paper, and recycled substrates. Also, PUR adheres strongly to glossy stocks, including those coated with a varnish, UV coating, laminate, or Mylar.

Increased Resistance to Page Pullout -

When compared to EVA binding, PUR binding offers up to 60% more resistance to pages being pulled out. This is particularly important for books that will see frequent handling, such as manuals, textbooks, workbooks, cookbooks, or children's books.

Greater Flexibility -

EVA glue might crack at the spine if too much pressure is applied, such as attempting to press an open book down flat. Conversely, PUR glue offers incredible flexibility and will maintain its structural integrity even when the book is pressed down firmly or opened very wide.

Better Performance in Extreme Temperatures -

EVA glue can become brittle when exposed to cold temperatures. This can cause the spine to crack. Also, because EVA glue can be reactivated with heat, it can soften in hot temperatures and the pages can come loose. However, books bound with PUR glue will remain intact whether the temperatures are well below zero or 300 degrees Fahrenheit.

Neater Appearance -

The superior binding strength of PUR allows less glue to be used than its EVA counterpart. This not only helps the spine of a Perfect Bound book maintain a uniformly square shape, it also minimizes the amount of cured glue that is visible after the books have been trimmed.

Other Benefits of PUR Adhesive...

> PUR is safe and non-toxic

> PUR is eco-friendly and free from Volatile Organic Compounds (VOCs)

> PUR dries clear and will not shrink

> PUR is resistant to moisture and humidity

> PUR is a one-part adhesive - not having to mix or measure ensures a consistent formulation

For adhesive-bound books, Color Vision uses PUR exclusively

As mentioned above, EVA glue is still widely used for creating Perfect Bound books. However, because the performance of PUR glue is vastly superior, Color Vision does not use EVA glue. When producing adhesive-bound books, Color Vision uses PUR exclusively.

If you are interested in all the benefits PUR adhesive can bring to your next book project, give us a call at 800-543-6299 and we'll be happy to help.

Or, if you would like to receive a bid for an upcoming project, simply fill out our Quote Request form and we will email our quote to you.

As always, we look forward to assisting with your printing and binding needs!

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