Design engineers working on medical and dental applications are always looking for new ways to package products. However, finding the right material and adhesive combination can be tricky. Cold-seal adhesive technology offers an alternative to traditional packaging techniques. Working with an experienced materials converter, design engineers can explore cold-seal alternatives at the beginning of the design phase to help avoid unnecessary changes later in the process.
Cold-seal adhesives are based on mixtures of adhesive components and natural latex rubber. Since 1999, the FDA has required that cold-seal adhesives that use natural latex rubber in medical packaging be labeled appropriately due to allergens attributed to natural latex rubber. To accommodate this ruling, synthetic rubber-based cold-seal adhesives have also been developed to take advantage of the low temperature, low cost, and bonding benefits of cold-seal technology.
Cold-seal adhesives are used for wound dressing applications and are usually available in paper film, transparent plastic film, and transparent carrier film and paper combinations. Cold seals are also available with sealing forces ranging from low at 0.5N/15 mm to higher at 4.0 N/15 mm. The low peel forces are desirable mostly for bandages applied to children.
Why use a cold-seal product? Cold-seal adhesives are a special type of pressure-sensitive adhesive (PSA) that forms a strong bond at room temperature with very slight pressure. Sometimes called cold seal, self-seal, or cohesive seals, they are applied to each of the substrates that will bond together. Cold-seal adhesives bond only to themselves; they exhibit no tack to other substrates. As a result, they don’t require a release liner. For some applications, this simplifies assembling materials within the paper packaging, without damaging the contents.
The base polymer used in cold-seal adhesive formulations must be able to bond to itself with only slight pressure and, at the same time, be hard enough to resist bonding to another substrate during storage and assembly. The polymers that provide the best autohesion characteristics include natural rubber, polyisoprene, butyl, and certain formulations of silicone rubber. Typical cold-seal formulations combine a natural or synthetic rubber elastomer (usually a latex) with a tackifier and other compounds.
Assembling the cold-seal package
For a typical cold-seal package, two separate pieces of cold-seal paper are printed. Then using a rotary press, the product is placed between the paper rolls, the layers of paper are squeezed together to form a seal, and the final package is die-cut to meet specifications.