There's a Glue for Every Purpose

by Gary Markovits, published in Printing News

There are hundreds of glues available for projects that require adhesive binding or spot gluing. Such a vast array of choices, however, is both a blessing and a curse. Selecting the right adhesive for a specific project can be a process scientific enough to warrant a degree in chemistry. Failing that, considerable binding and finishing experience will suffice.

Graphic arts glues can be broken up into two main usage categories: binding and cold pasting glues, and fugitive spot glues. Both of these categories place different demands on glues, and therefore require adhesives with different properties. We'll discuss the major glue options for each category, along with some tips on preparing pieces for different gluing operations.

Binding glues

The glues used in adhesive binding all have one common characteristic: they're designed for heavy, long-term use. They need to be strong enough to hold together hundreds of book pages and a cover, yet flexible enough to allow the book to be easily opened. Hot melt EVA (ethylene vinyl acetate) and PUR (polyurethane reactive) are the major adhesive binding glue families, and each has distinct characteristics.

Hot melt EVA binding glues are the "industry standard" perfect binding adhesives. There are literally hundreds of hot melt glue formulations, but there are common characteristics inherent to all of them. They offer a very strong bind, and set within a matter of minutes. Hot melt binding glues are ideal for most perfect binding applications, and provide a very long shelf life. However, they do have some limitations. They are not very flexible, and are susceptible to remelting or cracking when subjected to extremely hot or cold atmospheric conditions.

Hot melt padding glues are another form of hot melt EVA adhesive. They are different from hot melt binding glues in that they are very flexible, but not very strong. These glues are suitable for projects that don't have thick, heavy pages that will pull away from the bind after repeated use. Desk calendars and pads are bound with this glue, which allows the sheets to be easily detached.

The other major binding adhesive family is polyurethane reactive, or PUR glue. PUR offers even greater binding strength than hot melt glues, and with several more advantages. PUR adhesives are much more flexible than hot melts, offering "layflat" qualities. They can also be used to produce a wider range of spine widths. For example, at E & M Bindery we can produce a PUR perfect-bound book with a spine width of under 1/16"!

PUR glues are more durable than hot melts, and are able to withstand quite a bit more punishment. This makes them ideal for high-abuse applications such as high school textbooks and automotive shop manuals. Unlike hot melts, PUR glues will bind even with some ink or coating creeping into the bind area. The only limitation to PUR glue is its drying time. A PUR-bound book needs 24- to 48-hours to fully cure.

Pressure-sensitive glues are used to glue book cover hinges to the first and last sheets in the book block. These glues are different than those used for the bind itself, and are easy enough to work with to use on almost all adhesive binding applications.

Adhesive binding tips

Regardless of which adhesive binding glue you need for your project, there are a few design and layout factors that need to be addressed. Here are a few tips to keep in mind to ensure your project goes smoothly:

Knock out coatings – Paper coatings and excess ink that seep into the gutter can ruin a great book by compromising the quality of the bind. The ideal bind is raw paper fiber-to-paper fiber. To be sure your bind will last as long as possible, knock out inks and coatings at least 1/8" from the grind-off area, whenever possible.

Leave a glue trap – Many times, excess glue will gather at the foot of a perfect-bound project during binding, creating a mess as pieces sail through the binder. This can happen regardless of which binding glue is used. To avoid such a situation, layout perfect bound projects with an additional 3/4" trim-off area – known as a "glue trap" – at the foot. Most modern perfect binders are capable of stopping glue from collecting at the head and foot. However, it's still best to leave a glue trap, as it allows the operator to run the binder at full production speed.

Allow time for testing – Binders need to consider many factors when they select the proper glue for a particular project. In addition to testing different glues on printed samples, page pull tests performed on bound samples will ensure an appropriate bind. Be sure to allow your binder plenty of time to perform these tests.

Spot glues

Projects that require a dab or strip of glue to hold two panels closed need a different adhesive altogether. Spot glues are used on everything from direct mail pieces to point-of-purchase displays. Modern production technology makes spot gluing a snap. Everything from production inserts to credit cards can be applied inline with the proper feeders attached. At E & M Bindery, we can perform several kinds of spot gluing in-line with folding and cutting operations, all at full production speed. This not only saves considerable time and money, it yields a more attractive piece.

Spot glues can be applied using either a "cold" water-soluble formula, or a hot melt process. Since hot melt is the more common production method for most spot gluing applications, we'll stick to that as our basis for glue comparison.

Fugitive glue, also known to some as removable glue, is ideal for direct mail applications. It's designed to hold two panels together until they are separated by an end user, making it a suitable closure for a self-mailer. Fugitive glue can be removed without tearing paper fiber, and can be easily rubbed away after use. This makes it a good choice for applications that require glue to be placed in a visible location on the piece.

Remoist glue is what's found on the inside edge of an envelope. It is moistened and affixed by an end user, making envelopes and other return mail pieces the exclusive application for this glue. Cold and hot melt remoist application methods offer distinct advantages based on specific production needs. Cold remoist application isn't heat activated, making it ideal for pieces that will subsequently be sent through a laser printer. However, hot melt remoist dries much faster than cold application, which helps speed the project through subsequent production stages.

The third major spot glue variety is permanent glue, which is designed to keep two panels together indefinitely. There are several common applications for permanent glue, such as paste binding or affixing easels to create point-of-purchase displays. It's also used to tack two pieces together during subsequent finishing operations, such as die cutting. The glue is placed on extra material that will be trimmed off once the "tack" has served its purpose.

Tips for spot gluing production

Spot gluing offers its own set of production challenges from adhesive binding. Where adhesive binding is the placement of a glue on a specific location – namely, the edge of a book block – spot glues are placed anywhere and everywhere on a printed sheet. Here are a few tips to keep in mind when designing a piece that will receive spot gluing:

Make it laser-friendly – Glues must be chosen carefully for pieces that will be sent through a laser printer for personalization. Many hot melt glues will cause the sheet to pucker and curl when sent through a laser printer. Occasionally, "remelted" glue will seep from the edges of a piece, making a mess both inside the printer and on sheets that pass through it. Consult with your finisher to find an appropriate glue if you're producing a direct mail piece that will receive laser personalization.

Test it when necessary – There are myriad production and end use factors that come into play when selecting a spot glue. Warehouse, shipping, and destination climate; packing details; ink and paper chemistry; size and weight of the finished project; and even government regulations all need to be considered before placing glue on paper.

An experienced finisher knows which glue to use for just about every type of project. However, there is the rare difficult project that requires testing to be done to determine which glue will hold. If testing is necessary, be sure to send samples to your finisher well in advance of the project itself. Two to three days is usually ample time for your binder to test a variety of glues, pinpoint problems, and find solutions for those difficult projects.

Whether you're binding a book or sealing a multi-page self-mailer, there's an adhesive that will make the job a success. The trick is finding it! That's where it pays to involve your finisher early in the design process. Make sure your finisher knows every detail about the piece – not just how it's printed, but where it's going and how it will be used. This will make spot gluing and adhesive binding jobs much more attractive, save you time and money, and make the entire process worry-free.

Gary Markovits is President of E & M Bindery, Inc., a Clifton New Jersey-based trade binding and finishing company specializing in many types of post press services. E & M Bindery recently installed a new 12,000 book per hour Muller Martini Norm perfect binder, which compliments the company's existing Muller Martini StarPlus with layflat capabilities. Call Gary at (800) 7EM-BIND.

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