Pass Order Decides Which Effects Remain Achievable
Pass order determines surface energy, registration accuracy, recyclability, and unit scrap rates across multi-step print converting runs.
Alkaline De-Inking
Chemical Dispersion
Removal of printing media from waste paper relies on an aqueous suspension maintained at a basic pH level to facilitate the detachment of ink particles from cellulose fibres. Alkaline de-inking utilizes sodium hydroxide or sodium carbonate to swell the fibre and saponify fatty acid soaps that act as surface active agents during the flotation process. This reaction lowers the surface tension at the fibre-ink interface and allows air bubbles to carry hydrophobic ink aggregates to the surface of the pulp slurry for mechanical skimming.
Process Efficiency
Higher pH conditions improve the optical properties of the resulting pulp by increasing the brightness and reducing the count of visible contaminants. Sodium silicate addition during the operation stabilizes the hydrogen peroxide often employed for bleaching, which prevents the rapid decomposition of the bleaching agent and keeps the metal ions in solution. Excessive alkalinity might lead to fibre yellowing or chemical degradation depending on the wood species involved in the furnish.
Precise control over the concentration of caustic additives determines the yield of recovered paper and the load on the wastewater treatment plant.
Substrate Impact
Print quality on recycled substrates depends on the complete removal of non-impact inks and liquid toner remnants during the chemical stage. Residual ink particles cause specks that impair the performance of high speed sheet fed presses or digital print engines. Excessive chemical residues remaining in the final sheet surface might interfere with the drying profile of water based coatings or the adhesion of primers.
Optimal recovery results require a balance between ink detachment rates and the structural integrity of the recovered pulp fibres.