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The required quality of modern food packaging can be ensured only by combining several functions in it. The main one is, of course, the protection of the contents from harmful external influences due to the tightness of the package. Its attractiveness is also important, which serves as a kind of marketing lever, motivating the buyer to purchase the product. For example, due to the high moisture content, fresh meat requires constant cooling during storage on store shelves, which leads to the formation of water droplets on the inner surface of the covering film. As a result, the visibility of the contents of the package is impaired, which the customer, in turn, perceives as less fresh. The traditional solution to the above problem is the use of so-called anti-fog agents in the composition of the film material - additives that increase the surface energy of the coating film, usually made of polyethylene (PE), improving its wettability with water.

Due to this, not drops are formed on the surface of the film, but a thin and transparent layer of water, which does not interfere with viewing the contents of the package. Such antifogs are widely used today in mono- and multilayer food packaging. Usually, such additives are introduced into the surface layer of a multilayer packaging film, but due to migration, they are distributed over all its layers, which leads to a decrease in the anti-fog effect. In addition, in the presence of barrier layers made of polyamide (PA) or EVOH, the polar nature of these materials enhances the migration of antifog and leads to the formation of its agglomerates at the interface between the adhesive and barrier layers, impairing their adhesion.

Adhesives are an indispensable component of barrier packaging systems, providing adhesion between layers of materials of different nature in multilayer films, bottles, sheets, pipes, etc. To create structures that combine polyolefins and materials such as PA, EVOH, aluminum, etc. usually adhesives based on the same polyolefins, but grafted with polar functional groups of maleic anhydride (MA). In this case, the adhesive must be sufficiently elastic and provide proper adhesive strength both during storage of the film for at least six months, and at some stages of its processing, when it is subjected to high mechanical stress, as, for example, in processes such as double-bubble or triple -bubble. And, of course, a balanced adhesive should not interfere with the anti-fog effect.

Specifically for barrier films with anti-fog, Mitsui Chemicals has developed the NF358E ADMER series adhesive, which has an increased MA content to provide the necessary adhesion to PA and EVOH, and contains an inhibitor of anti-fog migration to the barrier layers. Thanks to this concept, the film produced with NF358E not only has excellent anti-fog and adhesion performance, but also its stability over time after extrusion. This has been confirmed by test results for barrier films with two different anti-fog agents. Fig. 1 and 2, it can be seen that in both cases, the indicated indicators are comparable, which cannot be achieved using standard adhesives.

Thus, ADMER NF358E provides both the required level of adhesion and the absence of influence on antifog, which makes it optimal for polyethylene coating films with antifog.

Figure: 2. Dependence of the peel strength F of the NF358E adhesive on the storage time t of barrier films with anti-fog agents AF 1 and AF 2 after extrusion.

Effective adhesive for barrier films: M. A. Tarantsova, Leading Sales Manager in Russia and the CIS, UTS Group

Effective Adhesive for Barrier Films M. A. Tarantsova

Advantages of the new ADMER NF358E adhesive of Mitsui Chemicals intended for use in the multilayered barrier packaging films containing antifog are discussed.