PE labels are the same polymer as the final product. These labels that remain with the PE throughout the recycling process, whether they detach or not, increase yield and have minimal negative quality impact for the reclaimer.
Of the available labeling methods direct printing adds the least amount of potential contamination. Small levels of the correct inks disperse in the final polymer without having much of an impact on quality. Heavily printed film of dark colors can be problematic since the dark colors affects a large amount of polymer, limiting its potential for reuse. The amount of printing should be limited since heavy levels of ink volatize in the extruder and may cause gels in the final product even if most recyclers use vented extruders. Large amounts of printing can overwhelm the capacity of these extruders to remove the volatile components.
Paper labels pulp and become a water filtration and contamination problem if they are processed through a wet recycling process. Individual paper fibers are very difficult to remove and attach themselves to the film creating specks and irregularities in the products made from recycled film. Furthermore, in either a wet or dry process they degrade in the extruder creating an undesirable burnt smell that cannot be removed from the recycled plastic. This significantly limits its reuse.
Metal foil labels
These labels should not be confused with metalized film. Metal foil labels are extremely problematic in two areas. First, they alarm metal detectors that are employed at the beginning of the recycling process to protect machinery. When this occurs, the entire package containing the offending part is discarded and landfilled. Secondly, if they happen to pass through the process into the extruder they can quickly blind a melt filter causing a pressure upset which automatically shuts down the process for safety.
REQUIRES TEST RESULTS
Some label inks or direct print inks bleed color in the reclamation process, discoloring the PE in contact with them and possibly diminishing its value for recycling. Since most recycled PE is colored, the impact of bleeding inks may not be significant; however, since the end use is not known beforehand, label inks should be chosen that do not bleed color when recycled. If inks redeposit on light colored or clear PE flake, this discoloring may diminish its value for recycling. Inks should remain adhered to the label and not bleed into wash water to avoid this potential discoloration.
Testing must show that adhesives will either wash off cleanly from the PE in the recycling process or be compatible with PE. Since typical film PE recycling process conditions are not aggressive enough to remove all adhesive material, a certain amount of residual adhesive is to be expected in recycled PE film. Adhesive residue that is not removed from PE during the wash step, for those film recyclers that use washing, is a source of contamination and discoloration when PE is recycled. Recyclers without wash systems may encounter melt filtration issues from adhesives. For these reasons, minimal adhesive usage is encouraged.
The APR is developing a screening PP/HDPE Adhesive Test to classify adhesive as either wash friendly, non-wash friendly and compatible with PE, or non-wash friendly and incompatible with PE. Companies that are considering label adhesives and are unsure of their compatibility with recycling should ask their suppliers to provide APR test results.