Producing remoistenable glue self mailers

Until the 1990s, sheetfed printers had little opportunity to sell products with remoistenable glue. Today, short-run remoistenable glue jobs are practical because current machines yield high-quality jobs at good production rates.

Both sheetfed and non-heatset web printers can now produce products with direct response reply devices and participate in profitable direct-mail campaigns.

There are primarily two ways of applying remoistenable glue. The older technology “cold application water-soluble remoistenable glue,” works by transferring glue to paper by either a wheel or a blanket. This process has two main advantages. First, heat by itself doesn’t activate it, which means it is downstream laser compatible. Second, glue application pads come in different sizes and run in various directions, which allows the efficient manufacturing of products such as three-sided “U” bar reply devices (reply envelopes that have remoistenable glue applied on three nonparallel lines) and stamps (a glued area wider than a typical remoistenable glue application head).

Unfortunately, there are some significant drawbacks with cold applied glue. First, it has to be run through hot dryers, which frequently cause excessive paper curling and cracking. Second, cold adhesives tend to be thicker right at the beginning of the glue strip. Sometimes this thick buildup takes longer to dry and forces operators to choose between having either brittle paper or semi-wet remoistenable glue that may stick to neighbouring sheets. And, third, a potential fire hazard is created when paper is left in the oven when conveyors stop.

Extruded glue

Hot-melt extrusion is the other way to apply remoistenable glue. It gives operators more control over the placement and appearance of glue strips as they’re being applied to the paper. Computer-controlled solenoids allow operators to precisely start and stop glue flow wherever necessary. For example, if a two-up piece is being glued on an 8½-inch side, our extrusion machine will detect the presence of paper and begin the glue flow ¼-inch away from the paper edge. Then, it will apply glue for 8 inches, stop for a ½-inch, apply glue for another 8 inches and finally stop the flow a ¼-inch away from the trailing edge.

Water-soluble glue applied on a pattern gluer can do this too, but because pattern gluers rely on timed entry rather than motion sensors, its application isn’t as precise. In addition, our hot-melt extrusion glue rarely curls the paper and generally has a professional appearance, while cold-applied glues look duller, may have ragged edges and tend to curl because moisture is being added to only one side of the sheet. A potential drawback of extrusion machines is that they can only apply remoistenable glue in parallel lines. This means that glue laid down in the shape of a “U” either needs two passes or two machines running at right angles to each other.

In-line application

Most remoistenable glue jobs are done in-line with other binding processes. For example, a bindery may apply remoistenable glue, stop-perforate the sheet, apply seam glue to form a pocket, fold it, apply clip seals, slit it, ink jet, tip-on a card and keep the job in mail-sort order…all in-line. Needless to say, in-line production greatly reduces turnaround times and cost, making non-heatset web and sheetfed companies competitive on many jobs. Whether the piece is a self-mailer or bound into another product, in-line production is a good value.

The key factors

The five key factors of a successful remoistenable glue application are paper, glue, ink, coatings and atmospheric conditions. Let’s take these one at a time.

Paper

Knowing the characteristics of your paper is important. Remoistenable glue rests on the surface of enamel stock yet is able to create a good bond when moisture-activated. Uncoated stock also generally works fine, but will normally require a heavier line of glue since it is more porous because it tends to seep into the sheet.

Glue

Understanding the difference between water-soluble and hot-melt glue is important.

Ink

Generally, remoistenable glue can be applied over ink with fine results, but problems may occur when activated glue needs to adhere to paper with 100% ink coverage. Be safe and plan your artwork so that remoistenable glue doesn’t require adhesion to heavy ink solids.

Coating

Remoistenable glue doesn’t adhere to paper coating such as varnish. If you’re planning on flood-varnishing a sheet, change the design to spot and knock out varnish from where the remoistenable glue strip is to be applied and to where it will be adhered.

Atmospheric conditions

In high humidity areas, it’s essential to apply water-soluble remoistenable glue in a climate-controlled environment. To be safe, include a moisture-absorbing packet in each box. These packets draw moisture out of contained areas and prevent remoistenable glue from unintentionally bonding. Even perfectly manufactured remoistenable glue products sometimes will unintentionally bond inside a hot truck.