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Gluing--Sticking With Direct Mail

March 1999
BY JACK RICKARD


Until the 1990s, sheetfed printers had little opportunity to sell products with remoist glue. Today, short run remoist glue jobs are practical because the current crop of machines yield high quality jobs at good production rates. Both sheetfed and non-heatset web printers now can produce products with direct response reply devices and participate in profitable direct mail campaigns.

There are primarily two ways of applying remoist glue. The older technology—cold application of water-soluble remoist 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's downstream laser compatible. Second, glue application "pads" can be different sizes and run in different directions, which allows the efficient manufacturing of products such as three-sided "U" bar reply devices and stamps.

Unfortunately, there are some significant drawbacks with cold applied glue. First, it has to be run through hot dryers, which frequently causes excessive paper curling and cracking. Second, cold adhesives tend to be thicker 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 remoist glue that may stick to neighboring sheets. And third, a potential fire hazard is created when conveyors stop running, if there is any paper in the oven.

Extruded Glue
Hot melt extrusion is the other way to apply remoist glue. These machines give 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 81⁄2˝ side, an extrusion machine will detect the presence of paper and begin the glue flow 1⁄4˝ away from the paper edge. Then, it will apply glue for 8˝, stop for 1⁄2˝, apply glue for another 8˝ and finally stop the flow 1⁄4˝ away from the trailing edge.

Water-soluble glue applied on a pattern gluer can do this, too, but since pattern gluers rely on timed entry rather than motion sensors, its application isn't as precise. In addition, extrusion hot melt glues rarely curl paper and generally have a professional appearance, while cold-applied glue looks duller, may have ragged edges and tends to curl, since moisture is being added to only one side of the sheet.

A potential drawback of extrusion machines is that they can only apply remoist glue in parallel lines. This means that glue laid down in the shape of a "U" either needs two passes or two machines running in-line at right angles to each other.

 

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