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Issue Twenty-two, Winter 1999

BINDING: Where It All Comes Together
Source: Graphic Arts Monthly (July 1981)

Very frequently, we confine our consideration of paper requirements and problems to the printing process, because we tend to regard printed paper as the final product. Obviously, this is often not true since much printed output is bound in some manner for its ultimate use. It all comes together in the bindery. At this final stage of assembly, problems can arise. They can stem from binding requirements neglected during the specifying and printing of paper, or printing requirements that may conflict with those of the bindery or make binding more difficult. Or, they may be problems peculiar to the binding job itself.

Thickness and Bulk
Basis weight and thickness relate to the maximum number of pages that can be folded into a signature. For example, it may be possible to fold a given 60-lb paper into 32-page signatures, whereas a 70-lb paper will require 16-page signature. As paper thickness is increased, it becomes necessary to fold into signatures with fewer pages to avoid folding problems related to thickness.

Thickness also relates to the ease or difficulty with which a book can be opened and its pages turned. For any given paper, its stiffness, the resistance it offers to being bent or flexed, varies as the cube of its thickness. For example, if its thickness is doubled, its stiffness will increase eight times. Consequently, as thicker paper is used it becomes more difficult to turn the pages of a bound book.

Grain Direction
Grain direction is always an important consideration in the bindery. It is desirable that the first fold be made parallel to the grain. It is a cardinal rule that the grain direction in the pages of a book be parallel to the bound edge or spine of the book. Grain direction perpendicular to the spine makes pages stiffer and more difficult to turn and lay down. Distortion and buckling of pages at the bound edge are much more likely to occur when the grain runs perpendicular to the binding.

Squareness and Strength
Sheets that are out-of-square can present serious bindery problems. Sheets originally out-of-square may not be troublesome during printing but can cause inaccurate folding and misalignment of printing, trimmed edges, and margins during binding. Paper should be trimmed to squareness prior to printing. Out-of-square sheets that originate during press slitting likewise can be troublesome in the bindery.

Paper must have adequate strength for applications like gatefolds and inserting, and to resist pulling away from staples, which leads to the detachment of magazine and booklet covers. Also, it must withstand the cutting action of binding threads, trim without the shattering of its edges and the breaking out of chunks of fibers or coating, and not block under trimming pressure.

Other problems that arise during or after binding relate to moisture and relative humidity. As paper loses moisture, its fibers become less pliable. Server moisture loss, which can occur during heat-set drying, leads to brittle paper that may crack at the fold. If this occurs in signatures delivered at the end of a press, it can be detected immediately and eliminated or minimized. However, if sheets are subsequently folded in the bindery, problems due to severe moisture loss may not arise until binding, at which time it is too late to go back and correct the cause of the problem.

Wavy or tight edges that develop due to uneven moisture regain or loss throughout the sheet area can cause wrinkling during folding. Moisture differences and imbalance remaining among the various signatures as they are trimmed and bound into a book can lead to post-bindery problems. As the various bound sheets regain moisture and individually condition to their environment, some will grow in size more than others. This results in page sections with stepped, uneven edges that no longer resemble the neatly trimmed edges of binding. Another consequence of severe moisture readjustment is buckling at the bound edge of the book.

Adhesive Compatibility
Adhesive binding requires that the hot-melt adhesive penetrate into and among paper fibers to form a strong bond. High-density, relatively nonporous papers such as coated papers are more difficult to adhesive bind than bulky, rough, and porous uncoated papers. Paper properties that allow formation of bonds between paper and hot-melt adhesives are porosity, smoothness, and receptivity to the adhesive. Adhesion of a coated surface and a hot-melt adhesive may relate to the chemical make-up of the coating and the extent to which the two chemically bond to each other.

To form a strong adhesive bond between the book body and its cover, the backbone of a book is roughened, notched, or patterned in some manner to increase the area for adhesion and to give greater penetration and binding strength to the hot-melt adhesive. If the bound cover is a coated paper, it cannot be roughened for adhesive penetration. Anchoring of the hot-melt adhesive to the unroughened coated surface depends mainly upon chemical compatibility.

Consideration of bindery requirements for paper must not be overlooked at the inception of the graphic arts product. Communication among the bindery, printer, and paper and other suppliers must exit to assure a most satisfactory final product. Remember, it is the bindery that brings the product to its final form.


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