Hot Melt Glue: Making it Stick

Hot melt glue has many uses in packaging. One popular use is gluing cartons or boxes closed after erecting and loading. One key benefit of glue is that it provides tamper evidency.

Except when it doesn’t.

This is how a properly glued carton should look after opening. The two flaps are glued strongly enough that they can only be opened by tearing the material. This carton has obviously been opened and cannot be re-sealed.

John R. Henry, Changeover.com

I found this carton (below) on a store shelf with the end flapping in the breeze. The glue applicator did not fail, the glue stripe is clearly visible. But something went awry.

John R. Henry, Changeover.com

There are several potential causes of this failure:

1. The adhesive does not adhere well to the varnished, metalized surface. A knockout, or window, of unprinted board would allow better adhesion.

2. The glue bead appears properly applied. If the flaps had been properly compressed, it would be flattened but it is not.

3. The glue may not have been hot enough. If it has set up (dried) before compression, it will look like there was no compression.

Unglued flaps are not always obvious. Conveyor rails may hold them closed until they are packed in the shipping case. Depending on how they are stacked on the shelf, the customer may not even notice until they get it home. The consumer who finds the box unsealed in the pantry may discard it and vow not to buy that brand again.

It is usually easy to fix this problem once it is identified.

It’s easy when you know.

Find out more about hot melt glue. It’s covered in Chapter 2 of my Packaging Machinery Handbook. Other chapters cover filling, flexible packaging, coding, and all commonly used packaging machinery. It is available on Amazon https://amzn.to/3kr4qj7.

Table of contents and chapter samples can be downloaded at https://packmachbook.com/.