Evaluating Pulp Yield Losses from Extrusion Coated Board in Industrial Hydro-Pulpers
Polyethylene-coated board yields drop 8 to 22 percent in industrial pulpers as unseparated fiber bundles exit screens bound to rejected plastic film.
Optical Dirt Count
Visual Inspection
Quantifying visible speck contamination on paper surfaces identifies unwanted particles such as residual ink, shives, bark and plastic debris. Automated quality control systems record an optical dirt count by scanning paper sheets under standardized lighting and applying thresholding algorithms. Standards ISO 5350 and TAPPI T 563 define dirt particles as visible spots contrasting with the surrounding sheet background, typically having an equivalent black area exceeding two-hundredths of a square millimeter.
Lower speck counts indicate higher cleanliness required for printing grades and food contact packaging.
Image Analysis
High-resolution digital cameras capture images of moving paper webs or laboratory handsheets under calibrated illumination. Software algorithms evaluate gray-scale intensity differences between speck pixels and the average paper background to determine particle size distributions. The system categorizes specks into size bins ranging from tiny dots to large dirt spots, calculating total speck area in parts per million.
Optical dirt count measurement eliminates operator subjectivities inherent in manual comparison charts. Modern online image sensors scan full web widths at machine speeds above fifteen hundred meters per minute, instantly alerting operators to pulping clean-up failures. Chemical deinking efficiency and disperser performance are evaluated by measuring dirt count reductions before and after processing stages.
Calibrated reference tiles verify camera exposure and contrast settings every eight hours.
Packaging Quality
Clean paper surfaces prevent visual blemishes that degrade package printing clarity and brand presentation. Food contact paperboard standards mandate strict limits on dirt area to ensure raw material cleanliness and product safety. High dirt counts trigger batch downgrading to non-critical packaging applications.