Nowadays, short run re-moistened glue and adhesive jobs are possible because of current high quality yields from machines that have good production rates. This was not possible until the 1990’s, and it makes selling product through direct mail campaigns much more profitable.
There are two kinds of adhesives used as remoistenable glue. There is the older technology, which is water soluble remoistenable glue that undergoes a cold application. It works by transferring glue to paper by use of either a wheel or a blanket. There were 2 advantages to this technical adhesives property: First it isn’t activated by heat, this made it laser compatible in downstream applications. Second, there are various sizes of glue application pads that can run in many different directions. This allows for efficient manufacturing of complex product.
Cold applied glue does still have some significant drawbacks. It has to be run through hot dryers after application. This will frequently cause the paper to curl and crack. For another, cold adhesives have a tendency to be thicker at the beginning of the glue strip. This thick build up can take longer to dry, which forces the operators to choose between semi-wet remoistenable glue that can potentially stick to other sheets, or dried out brittle paper. Lastly, leaving the paper in the oven for long periods is a fire hazard. All in all, it’s more risk and variables than are acceptable in a short run product.
Holt melt extruded glue is the other option for applying mesaproducts remoistenable glue. Operators have more control over glue placement, and the appearance of the glue strips as they’re being applied. This is done by computer controlled solenoids that precisely start and stop the flow of the glue when necessary.
Water-soluble glue that is applied on a pattern gluer can do this too. But since pattern gluers rely on timed entry, rather than motion sensors like the computer controlled solenoids of hot melt extrusion, the application is not as precise. There is also the fact that hot melt extrusion glue rarely curls the paper, and has a professional appearance. Cold application glue tends to look duller, and have ragged edges that curl because moisture is being added to just one side of the sheet. If you were looking for a drawback for extrusion machines, one would be that they can only apply remoistenable glue in parallel lines. If you have a pattern that needs to be laid down in the shape of a “U” you have to either do two passes, or have two machines running at right angles to one another.