Overview
ISO 8791-5:2020 specifies the Oken method for determining the roughness/smoothness of paper and board using air-leak techniques. Applicable to all printing papers and boards, this part of the ISO 8791 series defines the Oken smoothness measurement (expressed in seconds per 100 ml (s/100 ml)), the required apparatus, sampling, conditioning, calibration and test procedures for reproducible smoothness testing.
Key topics and technical requirements
- Measurement principle: Time for a fixed air volume to leak between measuring lands and the test surface is converted to Oken smoothness (see Annex A for principle).
- Apparatus types: Two permitted Oken tester configurations:
- Water column type - uses water-column manometer, capillary (≈0.3 mm ID, ≈50 mm length) and scale plate; constant pressure ≈4.90 kPa (500 mmH2O).
- Electronic sensor type - uses an electronic pressure sensor and digital display to report pressure and Oken smoothness.
- Measuring head: Loading weight and rubber plate (≥48 mm diameter) apply a clamping pressure of (98.1 ± 1.0) kPa. Rubber plate hardness: (50 ± 5) IRHD; rebound resilience ≥62%.
- Scale and calibration: Capillary length adjusted so constant K = 100; scale covers 0 s to ∞ s/100 ml. Calibration checks: zero reading 0 ± 0.01 kPa and leakage test pressure > 4.88 kPa (water-type adjustments described).
- Sampling & test pieces: Sample according to ISO 186; condition as per ISO 187. Prepare ≥10 test pieces per side (recommended 100 mm × 100 mm). Readings stabilized on scale/digital display; report mean smoothness to two significant figures.
- Precision & reporting: Annex B contains precision data. Standard deviation and coefficient of variation can be calculated when required.
Practical applications
- Quality control of paper and board surface properties for printing performance and coating processes.
- Supplier and incoming inspection of printing papers and boards where surface smoothness affects ink laydown, print uniformity and gloss.
- Research and development of paper coatings, calendering processes, and surface treatments.
- Acceptance testing in manufacturing, conversion and print-house environments.
Who should use this standard
- Paper and board manufacturers and mill laboratories
- Independent testing laboratories and certification bodies
- Printers, converters and packaging producers concerned with print quality
- Instrument manufacturers producing Oken testers and testing equipment
Related standards
Keywords: ISO 8791-5:2020, Oken method, paper smoothness, Oken smoothness, roughness testing, Oken tester, air leak methods, printing papers and boards.
Open preview (PDF)Paper and board — Determination of roughness/smoothness (air leak methods) — Part 5: Oken method