Like Goldilocks, packaging engineers search for carton or case sealing parameters and patterns that are “just right.” Advice from adhesives expert Pierce Covert will help you attain your fairy-tale ending.

Often you will attempt to open a package, a carton or corrugated cases and pull on it, and the entire major flap completely shreds in your hands. Most people aren't looking for that kind of bond. Instead, they are looking for something that will easily open and show fiber tear between the two flaps. When this bond has worked properly, it is sufficient to hold the box together to reach the end user who will open it in the store or at home.

The perfect glue pattern

In most case and carton erecting and sealing, hot melt thermos plastic adhesives are used to achieve the proper final package. These adhesives are often applied in bead form from multi-orifice, high-speed automatic glue guns.

The perfect glue pattern for these packaging applications uses a minimal amount of adhesive, sets in the perfect period of time and offers exactly the required amount of pull required to open the package flap. Usually you're bonding major flaps—the outside large flaps—to inside minor flaps. Normally, the adhesive is applied to the minor flaps. The major flaps are folded over, pressed against it and the adhesive sets.

Factors in glue application patterns

Pattern length, width, compression and type of glue all factor into using the correct amount of adhesive for a packaging application. Some customers will say, "This thing must be completely destroyed for somebody to get into it." In that case, we can flood the flaps with hot adhesive, but it will result in more cost.

Most customers, however, just want to secure their containers from point A to point B. They want the cartons and corrugated cases to open easily, but not so easily that receiving personnel cannot tell if the case has been previously opened.

With packaging, an important consideration is the correct fit of the material being placed in the package: over- or under-filled cases may require more adhesive to create a secure seal because of the additional pressure or lack of consistent pressure between the flaps that are being compressed.

Environments must also be considered, and are sometimes the most important of all. If products are filled in a hot area, or shipments pass through or arrive at hot or cold areas, the low softening point or incorrect adhesive quantity may loosen the bond causing flaps to pop up—a situation that would not occur in milder climates.

Packaging environments and equipment

So in some packaging environments, the correct amount of adhesive is dictated by inefficiencies in the packaging operation. For instance, if the corrugated case is not perfectly square or the compression system doesn’t do a perfect job of compressing the flaps, applying more adhesive may well compensate for those imperfections.

In theory, every package has an optimal amount of adhesive and perfect pattern to ensure a properly sealed box. However, in reality, inefficient packaging machinery and/or hostile environmental conditions can greatly increase the amount of adhesive needed to provide a secure seal. We have worked in applications where as much as 50% more glue was being use to achieve consistently strong seals, simply because the packaging line was comprised of old, highly inefficient components. Also, updating old hot melt machinery will go a long way toward eliminating excess glue.

Pierce Covert is the president of Glue Machinery Corp., which specializes in industrial hot melt adhesive application equipment used worldwide by a range of manufacturers.