Adhesives and Glues for Mailers
The name Hot Melt Adhesive comes from the word adhere and stands for sticking firmly to a surface or an object. Adhesives are therefore made to help you repair or even join different kinds of objects at home very easily. There are different types of adhesives that are made to specifically work with various surfaces.
Adhesives have a long list of uses. They are so inextricably linked to our lives that we become oblivious of their presence. We will find different kinds of adhesive used in every sphere of our daily lives when we look around, for instance, furniture, gadgets or toys. Their varied use in food packaging to building construction has forced the manufacturers to research and make different kinds to suit different needs. Some are toxic and strong, they serve industrial purpose. Some are mild and free of any kinds of toxics. They are used in making toys for children, infant products or edibles packaging. Some are water resistant and non toxic.
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. The first advantage is that it isn't activated by heat which makes 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 still has 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.
The other option for applying remoistenable glue is hot melt extruded 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 which is applied on a pattern gluer can do this too. But since pattern gluers rely more on timed entry, instead of motion sensors, 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.
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