INTRODUCTION – WHAT IS A PAPER BASED SILICONE RELEASE LINER?

Paper-based silicone release liner is the name given to the part of a self-adhesive label laminate which needs to be peeled away from the label itself before the label is then applied to the final article or surface. It’s role is to protect the self-adhesive part of the label before the label is applied to the final surface, at which point the release liner is no longer needed and ready to be recycled. Typical paper-based silicone release liners are based on a lightweight glassine paper which is coated with a thin layer (roughly 1 micrometer thick, or 0.001 of a millimeter) of a silicone elastomer.

RECYCLING OF PAPER-BASED SILICONE RELEASE LINERS

Paper-based silicone release liners, like many other grades of paper, can be (and indeed are already) recycled.

In some cases, this is occurring where the paper-based release liners are being collected together with other paper grades in large scale paper recycling processes. In some of these paper recycling processes there can be a challenge to break up the silicone coated paper, but provided that sufficiently energetic pulping conditions are utilized, the silicone coated release liner should be relatively straightforward to re-pulp. In this respect it is normally recommended to prefer batch re-pulping equipment over continuous re-pulping equipment in order to overcome the naturally hydrophobic nature of the silicone coating. The concentration level of silicone release liner which can be included in such mixed paper recycling processes varies significantly and depends on the process employed and the intended end application for the recycled paper fibres.

In other cases, the paper-based silicone release liners are handled using dedicated recycling processes where separated streams of 100% paper release liner are taken and recycled using optimized separation processes that have been specifically developed for the release liner. The benefit of this approach is that due to the high quality of the paper fibres used in the production of the base papers for silicone release liner (such as glassine), the high quality fibre that is recovered as pulp can be re-used for a wide range of paper grades including be recycled back into the production of glassine which can then be used as a base paper for release liner once more.

CASE STUDY – RECYCLING OF PAPER BASED SILICONE RELEASE LINERS IN A ‘DEDICATED’ RECYCLING PROCESS

Whilst there are cases today where paper-based silicone release liners are recycled at low concentrations with other paper grades in general paper recycling processes, the most successful recycling approach has been to recycle them in more specialized/dedicated recycling processes.

A current example of this process is the one being used by UPM PLATTLING mill in Germany. The Plattling paper mill receives a range of paper-based silicone release liners from a number of different industrial sources. One major source is the UPM-Raflatac “RafCycle” scheme where release liners are returned from end-users of Raflatac’s self-adhesive materials and there are other sources from industrial users of self-adhesive laminates and labels. These are mostly glassine based papers coated with silicone which have been used to carry self-adhesive labels.

After the labels are removed from the liner during the packaging operation, the rolls/sheets of glassine are then bulked together before shipment to Plattling’s paper mill. There may be some small differences in the grades of silicone coated glassine that are collected, both in terms of their basis weight or colour, but this is not usually something that would prevent their subsequent recycling. The colours typically used for glassines in label applications are generally ‘light’ colours (white, yellow, honey and light blue), which means they can be recycled together in the process. For the darker colours of glassine (such as ‘havana’/’Topaz’), which are typically used for other applications there can be significant problems to recycle with light coloured grades as these are based on ‘colour dyed fibres’ rather than a subsequent ink/coating which might have been removed in a de-inking process. These darker grades would need to be recycled in a separate process to avoid contaminating the other grades.

Contamination of the paper release liner by other materials such as filmic materials, self-adhesive labels and other non-paper contaminants can also pose problems in the recycling process but can still be ‘handled’ at low levels in the current process.