Impurity Screening
Stock preparation systems in recycled paperboard mills measure non-cellulosic matter present in recovered paper streams to protect processing machinery and finished sheet quality. Assessing mill secondary fiber contamination identifies plastic films, metallic staples, hot-melt adhesives, and wax coatings that enter pulping systems through collected post-consumer packaging. Coarse screens and fine slotted screens remove heavy debris and lightweight polymers prior to sheet formation.
This measurement establishes quality thresholds for incoming baled wastepaper but does not apply to virgin wood pulp furnish.
Process Disruption
Non-fibrous contaminants reduce mill operating efficiency by clogging screen plates and building up on dryer cylinders. When mill secondary fiber contamination exceeds operational limits, sticky adhesive residues form deposits that cause sheet breaks on high-speed paper machines. Unscheduled downtime for machine cleaning increases energy consumption and lowers total daily mill production output.
Chemical detackifiers and dispersants help stabilize micro-stickies in process waters to prevent agglomeration.
Quality Degradation
Undetected contaminants carried into the finished paperboard web compromise mechanical strength and print performance. Plastic specks and adhesive spots create void areas during ink application, leading to print defects and poor ink adhesion on converting lines. High levels of mill secondary fiber contamination also impair interlayer bond strength in multi-ply recycled boards, increasing the risk of delamination during scoring and folding.
Mills enforce strict bale inspection procedures and automated optical sorting to maintain secondary fiber quality. Controlling contaminant levels preserves board stiffness and runnability for demanding packaging applications.
