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Protection against mineral oil migration: Barrier coating on cardboard packaging

Paper is the most recycled material in the world. With good reason: using the paper fibre from wastepaper protects the environment and provides a valuable raw material. It also provides commercial benefits for many businesses involved in the cycle from production to recycling.

For instance, the paper and packaging industry uses wastepaper not only for image but also for cost reasons to manufacture all kinds of secondary packaging as well as bags or boxes for food. However, the recycled material usually has to be equipped with additional protective characteristics to prevent unwanted “side effects” such as the migration of mineral oil components from varnish or print ink residues into the product.

Food packaging made of wastepaper often attracts negative headlines due to the potential migration of harmful substances. The latest case in public focus is discounter Aldi Süd with its demand that private label manufacturers should take all necessary measures to prevent mineral oil contamination in food. The discounter addressed not only the packaging manufacturers but also all relevant suppliers, demanding practical solutions to ensure that there will be no more mineral oil residues in food products. Mineral oil residues in food are therefore an issue that concerns and affects the packaging industry, making an effective barrier absolutely essential for food packaging made of recycled cardboard.

Several packaging manufacturers have risen to the latest challenges and are equipping their production lines with corresponding coating systems. A number of different measures have already been developed for folding boxes: from an inner foil, a dispersion or extrusion coating on the inside, to a layer of activated charcoal. Processors in the packaging industry want an adhesive that is suitable to manufacture primary packaging as well as secondary packaging. To address this requirement, the Research & Development department of Jowat developed a general‑purpose adhesive, which is suitable for closing folding boxes made of recycled cardboard as well as for bonding corrugated cardboard for the outer packaging.

Bonding cardboard made of recycled paper is a process with special challenges. On the one hand, the quality of the raw material cannot be changed, which is why it has to be tested and selected to ensure the necessary homogeneity. On the other hand, many paper manufacturers are already applying a corresponding barrier. The different barrier coatings, however, are the knowhow of the cardboard manufacturers who keep the formulation of the coating secret. This makes it extremely difficult to assess and measure the characteristics of the cardboard surface. For instance, it is not possible to measure the surface tension with standard test methods, making it extremely difficult to evaluate the wetting property, which is essential for a reliable process. Jowat had to learn that the standard test procedures for fresh fibre paper do not work on recycled material. As part of the supply chain, the adhesive manufacturer has contributed significantly to a sustainable solution. Numerous tests were carried out on many different cardboard types from different manufacturers to develop adhesives that are optimally adapted to the individual process requirements.

The demands on the adhesive are diverse, depending on whether it is used for closing the primary packaging such as folding boxes with a barrier coating, or for bonding the secondary packaging. The primary packaging requires a strong adhesion and good cohesion at low counter pressure, while secondary packaging requires an adhesive with increased heat resistance and fast setting. This is rounded off by the different processing parameters of the used packaging technology with individual process cycles and individual time windows. Demanding development work in collaboration with the customer and extensive field tests are necessary to deliver an adhesive that fulfils all those requirements.

Jowat has already launched the first solution – an adhesive for bonding the flaps of primary packaging made of wastepaper – which is delivering excellent results on all possible formats, at different processing parameters and on the different barrier coatings of individual cardboard manufacturers. Recently, the formulation has been optimised to provide even faster setting times without a loss of adhesion to make the adhesive suitable for bonding secondary packaging made of corrugated cardboard and to meet the specific requirements of this application. In addition, the risk of processing the wrong adhesive by mistake is eliminated when the same adhesive is used to bond the primary packaging as well as the secondary packaging.

The new adhesive is currently in the pilot phase, to underpin the developmental work with practical tests. Tests on standard folding box units have already delivered impressive results such as good processing characteristics and minimal stringing.

As an adhesive manufacturer, Jowat plays a key role in providing a successful solution for the highly demanding task of developing a powerful adhesive suitable for all primary and secondary packaging applications. This is done by extensive development work and in close cooperation with customers and partners.

The professional article is published in the Magazine 'Verpackungs-Rundschau 7/2016' in German language. You can download the original article down below.