Figure 1: Dynamic mixing injection kits (left) and barrier packs (right) increase two component adhesive mixing accuracy. Credit: PPG Industries

Much adhesive innovation rightly occurs in product formulation - but manufacturers shouldn't miss opportunities by focussing too closely on that activity. It's easy just to put products into standard barrels, tubs or tubes. But even an adhesive with the best chemical formulation and most desirable physical properties when cured in ideal conditions might better serve its users' needs given improved packaging. And while several standard formats are available to achieve this, a recent competition held by an adhesive producer has underlined the benefits even more innovative packaging can bring.

Two-component adhesives are a particular adhesive type where packaging can be important. While, for many applications, bulk supply in standard containers like tubs is adequate, "proportioned kits" designed to make combining and mixing two part adhesive contents easier are common. ¹ Ranging from simple plastic pouches to larger formats, one container typically includes enough head space to accommodate and mix the other component into by hand. This requires careful material control in the packaging facility. Furthermore, hand mixing can introduce air, and leave material inside the kits, upsetting the mixing ratio. Operators might therefore add extra catalyst or hardener which, whether it's intentional or otherwise, would speed up the cure and affect the adhesive's performance.

Some speciality packaging options are available that avoid this through dynamic or static mixing. In dynamic mixing, adhesive components meet in a mixing chamber and are combined by a mixing element. For mixing ratios below 1:10 injection-style kits, the lower volume part is contained inside a valve mixing rod, while the base is inside the cartridge. Above that ratio, barrier kits, where two parts are separated by an aluminium foil barrier formed over the mixing head, can be used. These are typically available in sizes up to 500 ml, suitable for handheld gun dispensing.

Figure 2: Static mixing packaging, for example side-by-side cartridges, shown here, comes in a variety of sizes and formats. Credit: PPG Industries

Static mixing continuously meters and passes two streams of materials through mixing nozzles, comprising a series of mixing elements inside a tube. Package formats include side-by-side or coaxial cartridges, the latter having one cylinder inside the other, both used with extrusion guns. These are available for certain mixing ratios and volumes, typically 1:1, 2:1, 4:1 and 10:1 and approximately 35-500 ml. In such packaging, metering of the individual components to the mixer is crucial. That's in part because no shear action is involved, creating a chance that the materials won't be mixed enough, and also to avoid only one component being dispensed. Adhesive can also sometimes cure in the tip, causing "blow-by" blockages that can push adhesive leaking past the plunger in the back of the cartridge.² Dual syringes are also available for low-to-medium viscosity adhesives with ratios between 1:1 and 2:1, with mixing achieved either by nozzle or stick or spatula.

Figure 3: A finger applicator allows instinctive glue spreading without getting sticky fingers. Credit: Henkel Adhesive Packaging Design Contest

But now, thanks to the competition for creative adhesive packaging ideas, a new possibility has been highlighted for two-component adhesives.³ One prizewinner designed an "Epoxy Vial" that keeps the resin and hardener separate in two small chambers until they are brought together by slightly squeezing the pack. A slim nozzle at the point of the vial then enables precise application. Another category in the competition also looked specifically at opening and closure. In this area the prizewinner was an attractive "Daisy Magnetic" design, where individual adhesive portions are shaped as six petals of a plastic daisy. The daisy is magnetic so that it can be fixed to a refrigerator door, for example. The overall winner came from the "adhesive dosage and application" category, in the form of a drop-shaped rubber bottle called "Glue drop". The bottle comes with an applicator in the shape of a tube that fits over the finger, allowing even and instinctive adhesive application without the risk of sticky hands.

As well as packaging, integrating adhesives directly into products can sometimes be the best way to use their performance strengths. In the most extreme cases, the right product format can rescue adhesives no-one thought would ever make the market. At least that's what happened with the first and most famous brand of repositionable sticky labels.⁴ That product that became a household name. If thinking about how an adhesive's supplied can do that, perhaps it's worth some of your company's time to consider?

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