"Adhesives in the Finishing Process: Part I"
[Column #61, 1/00]
For those of us in the binding industry, it is common knowledge that glue can be a sticky issue. As with many other tools we use each day, there are several choices on the market with a range of properties useful in different applications. Understanding these differences and selecting the appropriate adhesive for a given finishing job is a critical part of the planning process.
Most of us seldom think about the many products we handle each day that contain some type of glue. It’s big business and it moves quickly. According to Myrna Block, contributor to this article and Vice President of Basic Adhesives in Brooklyn, New York, which provides a full range of water- and solvent-based adhesives to the graphics arts industry, “The adhesive industry is constantly changing and improving its products to keep up with the enormous pace of the United States Postal Service, the Environmental Protection Agencies, the high speed printing equipment available today, the progressive design industry, and the recycling industry.”
This two-part article will cover four of the most common adhesives used in finishing processes today: fugitive, removable, remoistenable, and resealable. Because of space limitations, I will cover the first two in this issue and the remaining two in next month’s issue.
Fugitive glue, or getaway glue, as it is sometimes called is most often used to temporarily join two pieces so that certain finishing operations can be performed. For example, if your bindery needs to temporarily attach a membership card to a direct mail piece that must be folded and inserted into an envelope, a fugitive glue can keep the two pieces together during folding. Paper choice is critical in this process as the two pieces that are joined must be similar in makeup; for example, coated paper to coated paper or uncoated paper to uncoated paper. A plastic card cannot be attached to a paper substrate. (This is done with an adhesive called removable glue, a topic covered later in this article.)
Fugitive glue is often water-based, has a high alcohol content, and is applied wet at a glue station to the substrate or host document (in this example, the direct mail piece). The guest document (the card in this example) is then placed on the host. The glue holds long enough for folding and other operations to take place. Later, it evaporates leaving no damage to either document and no residue.
Removable glues, on the other hand, do not disappear and are used for attaching two items together until the seal is manually broken by the end user. For example, credit cards are often attached to a carrier sheet for mailing. Once the card recipient receives it, he or she simply peels it off the sheet.
Removable glue is available in hot-melt or cold liquid form, is often latex-based, and is good for one-time sticking. It has the consistency of rubber cement and, once it has served its purpose, can be peeled off documents without leaving a sticky residue.
Removable glues have a wide range of applications. A few spots or a continuous line of glue can be used in place of sticky-backed wafers to seal brochures or direct mailers; the adhesive can also be applied in a pattern, such as a circle or square. Unlike wafer seals, removable glues can be applied in-line decreasing finishing time, and they do not damage either the host or guest document when the piece is opened. Wafer seals often tear the paper when the seal is broken. (There may, however, be a slight discoloration on the paper where it was applied.) Where the piece has multiple pages, such as a multifolded brochure, wafer seals are sometimes a better solution because it is impossible to apply enough removable glue to the sheets for effective adhesion.
Removable glues are also used for tipping one piece to another, such as attaching a customer reply card to a magazine page or affixing a sample pack of shampoo to a promotional handout. At Bindagraphics, we use a special machine called the Attacher to stick just about any two objects together. We can affix decals, magnets, pencils, tokens, embossed or thin-mil cards, coins, keys, brochures, blister packs, and reply devices to sheets, signatures, envelopes, and other host documents.
Removable glues are flexible, but certain factors determine how they should be used. For example, hot-melt removables set up faster and have a stronger bond than cold glues, making them a better choice for affixing heavier objects such as pennies or keys to a carrier sheet. Hot melts are also a better choice if both host and guest pieces have coated or otherwise slick surfaces because cold glue would never dry properly in such cases. Generally speaking, cold glues work well for lightweight objects and for a combination of coated and uncoated documents.
Since all types of glue need to grab onto something in order to be effective, porosity of the elements is a determining factor in glue choice. In removables, for example, both hot melt and cold varieties tend to stretch and even pop off a flood-varnished or ink-covered sheet. With some heavy paper stocks, such as vellum, a highly viscose (or thick) glue is a better choice than a thin one for maximum adhesion.
In next month’s issue, I will cover remoistenable and resealable adhesives.
Adhesives in the Finishing Process: Part 2