Handle With Care
Traditionally, bookbinding has been a relatively simple operation. But, as in many industries, competition has become fiercer than ever. For many book manufacturers, this competition launched a race to apply quality manufacturing methods and standards, such as Lean or Six Sigma, to the bookbinding operation in order to reduce waste and working capital, increase inventory turns, or improve productivity.
Ironically, while great progress has been made in decreasing turnaround time from publishing to book delivery, several book manufacturers report increased numbers of rejections due to poor quality, despite advanced manufacturing techniques. And as every book manufacturer knows, a 'good' book is one that doesn't come back.
Many quality gurus lack a proper understanding of what happens to cover board during a bookbinding operation. Since cover board is a natural fiber, it responds to natural elements—particularly moisture—in different ways. For example, "cover curl" occurs when the covered panel of a case-bound book does not remain flat, and it's a major issue in cover quality.
Cover curl typically increases during dry, winter months. Modifying your standard approaches to manufacturing during the winter months might help control cover curl and increase overall throughput.
In cold, dry weather, manufacturers need to compensate for lower humidity, but often don't. Cover board typically loses some of its internal moisture as the air becomes drier. This is evident when the top board units of an opened pallet start to curl upward in a cross-grain direction. The curling effect is natural with cellulose fiber, but sometimes leads to feeding difficulties on the case-maker.
When board is delivered from a cold warehouse or off the back of a truck, it needs to be acclimated to the manufacturing environment. Here are some questions you may want to ask your binder:
1 Does your binder store board in an environment similar to the manufacturing area?
2 Does your binder stabilize the board's temperature within 15º of the case-making area?
3 Does your binder open board loads to remove stretch film, but allow the board to be top-weighted while it acclimates to the temperature to minimize moisture dissipation?
4 Does your binder prevent air from blowing onto the board load during
case-making? In many situations, an overhead fan creates excessive air movement and accelerates moisture migration.
PENETRATING THE SURFACE
Case-making is a two-step process. First, adhesives are applied to the cover material and, depending upon the material's absorption ability, may sit
on the surface before penetrating the cover material. In step two, the cover board is placed on the cover material where the adhesive penetrates the
The process is called a moisture event, which can lead to curling if absorption or dissipation properties between the substrates differ.
Moisture acceptance varies widely depending on what types of cover materials are used. Film-coated and liquid-laminated covers won't have the same absorption or dissipation rate as natural cloth or uncoated paper-based covers because the outer side of the material is sealed.
Synthetic cover materials rely on a suction bond and have a limited amount of moisture acceptance. Regardless of the type of material used, the moisture from the adhesive goes into the board, resulting in additional fiber swell, which requires more time for moisture dissipation.
Depending upon the cover material, its level of moisture compatibility and the characteristics of the board, it may take anywhere from 12 to 24 hours to reach equilibrium with the environment. During this time, the bound book and the made cover can be manipulated or allowed to find equilibrium by stabilizing the bound book.
BOARDING THE BOARD
Add weight to maintain flatness during storage by stacking the same size covers on a supported flat surface during the 12 to 24 hours it takes to reach equilibrium. Brick stacking is the most common of a variety of methods used to stabilize made covers during equilibration.
The process requires each cover layer to overlap using a wooden top to weight the top layer to maintain flatness. For successful brick stacking key elements are:
a) Maintaining a consistent stack height that provides minimal weight build on the cover turn-in area,
b) Placing cover stacks so their weight is distributed to the outer edges of the stack below, and
c) Overlapping layers to stabilize the pallet for movement to the next operation.
If made covers are not controlled during equilibrium and there are dissimilarities between the bonded substrates, cover curl can result.
The rate of moisture intake and dissipation between cover material and cover board represents one consideration.
The other is the adhesive. The more adhesive that is applied, the more that moisture can affect substrate interaction. If the adhesive-solids content is low, additional moisture is added, and that moisture must eventually dissipate. Proper and timely stabilization of made covers reduces these variables.
In-line case-making and case-in operations pose slightly different equilibrium issues. As long as there is minimal time between case-making and case-in, the made cover won't have time to react to the moisture intake, reducing the chance of the cover curling before it reaches the case-in cover hopper. Problems occur when the case-in portion of the in-line operation is down and product continues to run .
This is prevented when made covers are brick-stacked, stabilized and fed back in-line without presenting problems to the case-in cover hopper.
LIMITING MOISTURE EVENTS
During case-in, application rollers apply adhesive onto the outer end leaf. As the adhesive on the end leaf makes contact with the exposed surface of the cover board, another opportunity for a moisture event exists.
In this case, the moisture from the water-based adhesive will begin penetrating the end leaf fibers and the board fibers. Another 12- to 24-hour period is necessary to dissipate the moisture and for the substrates
to reach equilibrium with the environment.
During this time, the bound book and the made cover can be manipulated or allowed to find equilibrium by stabilizing the bound book. This is frequently done by stacking the books onto pallets and weighting them with a pallet or light banding.
If books are packed directly after case-in, a properly fitted bulk carton will stabilize the bound books.
Proper handling within the process and understanding of the components are vital to manufacturing high-quality books. It is best to consider how changes to the environment, the types of cover board or cover material, glue, or stacking method will affect moisture dissipation. In this way, returns and allowances are kept to a minimum, improving overall book-manufacturing productivity.
– David Bird
David Bird is technical support manager of Rock-Tenn Co., paperboard products division, a binder board manufacturer in Norcross, Ga.