ISO 5350-4:2006

Overview

ISO 5350-4:2006 specifies an instrumental reflected-light method for estimating visible dirt and shives in pulp sheets using the Equivalent Black Area (EBA) concept. The method quantifies the visual impact of contraries (dirt specks and shives) within a physical area range of 0.02 mm² to 3.0 mm², reporting results as number of contraries per m² and EBA (mm²/m²). This part of ISO 5350 is applicable to both virgin and recycled pulp and complements other parts of ISO 5350 that use transmitted light or visual inspection.

Key topics and technical requirements

• Measurement principle: Instrumental reflected-light inspection uses an analyser that computes the EBA - i.e., the visually equivalent area of a standard black dot that produces the same visual impact as the contrary on the sheet.
• Scope limits: The EBA algorithm in ISO 5350-4 is limited to contraries up to 3.0 mm² physical area and is not suitable for direct physical-area measurements without alteration of equipment or algorithms.
• Specimen brightness: Sheets should have a brightness ≥ 30% (ISO 3688). Rough or corrugated mill sheets may need reformation into laboratory sheets.
• Detector and imaging: A densitometric detector with at least 256 grey levels and a fine pixel resolution (effective pixel area ≤ 0.020 mm²; standard cautions against going below ~0.002 mm² to avoid false detections) is required. Illumination should be diffuse, visible-spectrum (≈380–740 nm, peak 500–600 nm) with incident angle ~45° ±5° and uniformity within ±4%.
• Calibration: Certified matte calibration plates (white, black and dot patterns) with supplied Y-reflectance correction factors are used. Calibration includes zero and span adjustments (black and white GL targets) and EBA verification of dot arrays (results should agree within ~10% of plate certificates).
• Sampling & procedure: Representative sampling per ISO 7213; typical inspection involves multiple sheets totalling a specified exposed area (standard examples include mill and laboratory sheet procedures). Equipment warm-up and repeatability checks are mandatory.

Applications and users

• Who uses it: Pulp mill QA/QC teams, laboratory technicians, instrument manufacturers, and purchasers/end-users assessing pulp visual quality.
• Practical uses:
  • Routine quality control of pulp for graphic or specialty papers where visual appearance matters.
  • Comparative vendor or lot acceptance testing for recycled and virgin pulps.
  • Process troubleshooting where visual dirt load affects downstream paper-making performance or product aesthetics.

Related standards

• ISO 5350 (Parts 1, 2, 3) - other pulp dirt and shive estimation methods
• ISO 3688 - brightness (diffuse blue reflectance)
• ISO 5269-1 / ISO 5269-2 - laboratory sheet preparation
• ISO 7213 - pulp sampling

Keywords: ISO 5350-4:2006, Equivalent Black Area, EBA method, pulp dirt estimation, instrumental inspection, reflected light, pulp testing, recycled pulp, calibration plates, detector resolution.