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Board Warpage: True culprit may not be your board
The below was written by Werner Rebsamen, a bookbinding expert and a professor at the Rochester Institute of Technology.
As I write this article, it is wintertime again. Our indoor environments are heated, the air is dry. At the Rochester Institute of Technology book testing laboratory, samples of hardcover-bound products from all over the world arrive in numbers, all seeking an answer to what caused the board to warp.
The record is held by a book bound in Asia. The large hardcover-bound volume is only a 1/2" thick. But, in January, its front cover will warp to a height of 4 1/2"! It is the most severe cover warp problem an American publisher did ever encounter-40,000 copies. Ironically, the title of the book is "Texas!". (Is not everything the biggest in Texas?)
Recently, a New York City publisher wondered why, all of a sudden, the new delivery of his thin, hardcover-bound children's books were warping uncontrollably, making this product unsaleable. We advised the publisher that his printer/binder in another part of the world changed the paper grain direction. As it has self-contained endpapers, the wrong grain direction affected the stability of the cover.
Cover warpage is not exclusive to hardcover-bound books. It affects all products which have paper mounted over paperboards. Books, looseleaf binders, pre-made covers for desktop bindings, game-boards, etc.
Interestingly, some board manufacturers claim that their board is more warp resistant than that of their competitors. They may have a point in regard to internal stability. My experience as a bookbinder and trade consultant with 47 years of experience may differ from these statements.
While setting up the world's first fully-automated book manufacturing system (a set-up which included printing and hardcover in-line), we encountered severe cover warpage, even with the finest, most dense binders boards. This was caused due to dryness within the book block. These days, the book are no longer produced in-line for this reason.
It would take too long to explain all the various board qualities and causes of warpage. I have done that in other published articles. Therefore, let us be brief and try to understand this complex problem in layman's language.
A) All paperboards are subject to warpage. Some boards may be more resistant than others to warpage.
B) Warpage is caused not by the board itself, but by unequal forces mounted onto the board.
John Cole, a well-known expert on paperboard manufacture, stated it once very clearly: "Warpage is less likely to be caused by the board itself. We have traced part of the problem to cover materials, but we (the board people) don't understand the mechanics of the problem."
John Cole could not have said better. Board warpage is a bookbinder's problem. It has very little to do with the paperboard itself as long as quality paper-board products are used.
Having consulted around the world on this topic, I have encountered all board qualities, yet managed to get them all relatively flat using my bookbinding skills. For example, some will claim, the reason why there is warpage is that the moisture content of the board itself was not correct. It is usually around 8%. In China, during hot and humid summer days, we use paperboards with a moisture content of more than 15%!
The Book Manufacturers Institute once conducted an intensive study on cover warpage. The final findings of this study were as follows:
Why do boards warp? The basic cause of warp is moisture being absorbed or released. Unbalanced expansion or contraction of any materials compromising the cover relative to each other or within themselves can manifest itself as warp. To control warpage one must learn to control the rate of expansion or contraction of the components (called hydroexpansivity) or control the moisture in the system.
How can one understand the forces which cause paperboard warpage? Take a piece of paper-board and mount a thin piece of paper onto one side with a water-based adhesive. The paper will expand, the board will expand on its surface. The next day, the board will warp in the opposite direction as the paper did shrink and pull the board with it.
Try the same, mounting paper onto both sides, using the same grain direction and amount of adhesive. The paperboard will stay flat. Now experiment with different paper grain directions and amounts of adhesive. The boards will warp! In other words, one must learn to control and equalize the forces placed onto the paperboard.
There are two different theories out on the market to prevent board warpage; one that stresses density, another that stresses bulk. They are both correct if tested above.
What counts in paperboard quality I its method of manufacture, consistency and selection of fibers. Boards manufactured to a high-quality standard remain stable internally under all environmental conditions.
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