"Judging a Book by More than it's Cover"
[Column #14, 2/96]
Glues just aren't what they used to be. When we were kids, I remember there was only one option, Elmer's. Today, there's a whole world of glues . . . and a whole world of information to know about them; especially, if you happen to have clients who come to you for bookbinding.
But as important as learning about glues is finding out as much as possible about the end use of the book itself. And here's where you come in.
There's nothing like a horror story to prove a point, so here's one I hope will, ahem, stick.
End use. Many of our clients publish small-format books, you know, like those little perfect-bound map books available at roadside gas stations. On one occasion, we bound some books using a hot-melt glue, per our customer's instructions.
As with all binding jobs, we pulled books for testing throughout the run and logged in the results. They met our standards, which far exceeded what we all default to: the GPO (Government Printing Office) acceptable quality standards. We shipped 'em out.
Well, several weeks later, this was in summertime, we got a phone call. My customer was tearing his hair out because all his books were being returned, the pages had completely detached from the binding. I asked where they were being shipped back from. He said all the returns were clustered in the southern states.
That little piece of information could have saved the job. We all know, summers in the South are typified by high humidity and temperatures often well above 100F. Many of the people mentioned they had left the books on the rear window ledge of their cars, where they baked at even higher temperatures. Also, since the books contained maps, the users regularly bent the book in half backwards. (We have a test that measures a book's ability to endure this abuse; it's called the subway test.)
Clearly, the hot-melt glue was not up to the task. A PUR glue, or even Otabind, which uses either PUR or cold glues, would have been a better choice. The sad part is we could have told our client that ... had we been consulted.
Stress testing. Just as there are no industry-wide, agreed-upon standards for printing, finishers have to rely on their own resources to test for quality. My company, for example, has a battery of equipment to test the strength of books.
One machine measures the pounds of pressure a page can withstand before it is either torn or pulled from the binding. This is known as a page pull test . The equipment mechanically grasps a page and pulls, gradually applying more and more pressure. Generally, PURs withstand these tests better than hot-melts. Minimum standards are 2.5 lbs. per linear inch of spine. PURs routinely take 4 to 7 lbs. per linear inch to be dislodged. Hot-melt glues generally take 3 to 4 lbs. per linear inch.
According to Chuck Cline, Technical Manager of National Starch and Chemical Company's bookbinding division, If everything is the same-paper stock, spine preparation, application, everything-then EVAs will test at one level, rubber-based hot-melts will test 10-20% higher than EVAs, and PURs will test 20-30% higher. Of course, Mr. Cline cautions to consider all factors. For instance, the glue is only as strong as the paper. If you are using 40# stock, most adhesives (if applied properly) test out stronger than that and, therefore, the paper yields before the glue.
Another piece of equipment we use simulates a person turning a page back and forth by mechanically pulling a book leaf in 120 arcs. Called a flex test , it measures the number of turns a page will withstand before breaking from the spine. Again, PUR and other cold glues hold up better than hot-melts in this test. Minimum standards are 200 pulls. Conventionally bound pages generally withstand 300 to 400 pulls. Our bindings routinely test in the thousands of pulls.
Otabind, by the way, which is often mentioned in perfect binding discussions, outperforms PUR and hot-melts in flex tests. It is, however, specifically designed as a layflat perfect binding process. Otabind tests have shown their products to reach a phenomenal 34,000 pulls before a leaf is pulled out of the binding; whereas other processes average about 400 pulls.
Temperature tests measure the resistance of glues in varying climates by pulling pages after a book has been subjected to extreme climate conditions. Hot glues are weaker in this test, as well, because they tend to crack under extreme temperatures, causing pages to break away from the binding. In sample tests, PUR temperature resistance ranged from -40F to 200+F; whereas, a typical EVA had a range of 10F to 120F, emulsions - 40F to 120F, and rubber-based hot-melts -20F to 130F.
Here's a basic rule of thumb. When measuring the tensile strength of adhesives, liquid glues average 300 psi (pounds per square inch), EVA and hot-melts log in at 500-800 psi, PURs test 1600-2200 psi, and your average paper tensile strength is 50-80 pounds per square inch. So, remember that specific glue tests are only one factor when choosing a binding method.
Some basics. Perfect binding adhesives fall into three main categories: hot-melt, PVA (polyvinyl acetate) and PUR (polyurethane reactivate) glues. What follows is a brief review of these binding glues and their comparative strengths and weaknesses.
Hot glues are the most traditional method of binding. They are relatively inexpensive, cure quickly and form a good strong bond under most conditions. They tend to stiffen when cooled and, thus, do not hold up well under temperature extremes. It is difficult to incorporate hot-melts with the use of heavily coated stocks or stocks over 70# weight.
PVA is applied cold. When it dries, the resins penetrate deep into the structure of the paper stock, forming a solid bond. PVA glues cure to a semi-soft state, providing a more flexible backbone than hot-melts do. They also won't crack in extreme temperatures the way hot-melts do. However, in terms of page pull strength, they can't compare to PUR glues.
PURs are considered by most to be the most flexible and durable bookbinding glue on the market these days. They yield products that lie flatter and require less backbone preparation than other glues. On the flip side, PUR is more costly than other methods and the curing time is between 24 and 48 hours, a definite disadvantage if expense or turnaround are an issue. (But don't throw in the towel on the cost factor! Our friends at National Starch, the only company in the US who sells PURs to the bookbinding industry, have let it slip that Î96 promises some new economies for PUR.)
Equal to knowing the basics, you also need to be concerned about how glues hold up under various conditions. This information is critical to choosing the right glue and binding method. You and your client should consult with your finisher to determine the best glue and binding method, before specifying a project. Any finishing house worth its salt routinely tests its books and should have results readily available to customers. We test all books before and during runs and maintain logs of results. This enables us to continuously monitor the performance of adhesives, particularly important when we receive new batches of glues.
With many publishers planning for worldwide distribution, and given today's competitive market, bookbinding glues have to perform ever greater feats. Software publishers, for instance, have to pay particular attention to end-use, since their manuals can end up anywhere in the world. They must be able to stand up in a wide range of climates and user habits.
Even domestic publishers have to be knowledgeable about binding methods and durability. Books not only must catch a buyer's eye when on the shelf, but also they must be able to withstand a lot of abuse. Adding factors such as cost competitiveness and turnaround time, there's a lot to consider when selecting a glue for a project.
Choosing the perfect glue for the perfect binding isn't always easy. You and your sales force must be armed with at least basic information about glues and binding methods. And you must get and communicate as much information as possible about a bookâs end use and end-user. This is critical to making the right selection. In short, do your homework, then find a finisher who's done his.