Photoinitiator Migration Limits in Food Contact Print Finishes
Photoinitiator migration limits demand complete photopolymer conversion or functional containment to keep extractable residues below 10 parts per billion.
De-Inking Score
Recycling Metric
Quantitative assessment of the ease with which printing inks can be separated from recovered paper fibers during the recycling process is essential for high-quality paperboard production. This evaluation, summarized as the de-inking score, measures the brightness and color of the recycled pulp after the flotation stage. It determines if the recovered fibers are suitable for producing graphic paper or white-lined chipboard.
This measurement prevents highly contaminated batches from entering the paper machine.
Evaluation Technique
Spectrophotometric analysis of the pulp sheets determines the remaining ink spot area and the overall dirt count of the recycled fiber. Low values for these parameters translate to a high score, indicating that the ink was removed effectively. Conversely, stubborn UV-cured inks often yield a low score due to their cross-linked networks.
The resulting pulp might then be downgraded for use in corrugated medium or greyboard.
Fibre Recovery
Improving this score requires careful selection of ink formulations and paper substrates during the design phase of the printed carton. When water-based or flexographic inks are used, they can disperse into particles that are too small for flotation, which lowers the final score. In contrast, offset inks typically form larger aggregates that float off easily.
By testing printed samples prior to full-scale production, converters can select the best combination of ink and board to meet recyclability targets. This score guides paper mills in purchasing raw materials that will not compromise the optical quality of their recycled paperboard products.