Overview
ISO 5626:1993 - "Paper - Determination of folding endurance" specifies standardized methods for measuring the resistance of paper to repeated folding. It covers four widely used folding testers: Köhler‑Molin, Lhomargy, MIT and Schopper. The test principle is simple: a narrow strip of paper is folded backwards and forwards under a longitudinal stress until it fractures. Results may be reported as folding endurance (log10 of the number of double folds) or as the fold number (antilog).
Keywords: ISO 5626:1993, folding endurance, fold number, paper testing, Köhler‑Molin, Lhomargy, MIT, Schopper.
Key topics and requirements
- Test principle: Repeated standardized double‑folds of a narrow strip under a set tension until break.
- Specimen geometry: Test strips shall be 15 mm ± 0.1 mm wide; length sufficient for the instrument used.
- Instrument limits: Köhler‑Molin, Lhomargy and Schopper - applicable to paper up to 0.25 mm thickness and tensile strength > 1.33 kN/m. The MIT tester has interchangeable heads to accommodate thicknesses up to 1.25 mm.
- Tension and loading: Typical tensions indicated (examples in the Standard) include 9.81 N as normal; alternate values (e.g., 7.85 N, 4.91 N) are allowed if justified and reported.
- Number of tests: At least 10 readings per principal direction (machine and cross).
- Reporting: Either mean folding endurance (log10) to two decimal places or fold number to appropriate significant figures; include standard deviation, min/max, number of tests, instrument type, conditioning atmosphere, tension applied and other influencing factors.
- Environmental control: Condition samples per ISO 187; conduct sampling per ISO 186. Monitor temperature near the folding head - temperature rise should not exceed 1 °C after 4 hours of operation.
- Precision: Typical repeatability and reproducibility are provided (repeatability ~8% at low values decreasing to ~2% at high values; reproducibility ~10% to ~4%, depending on magnitude).
Applications and users
ISO 5626:1993 is used for:
- Quality control in paper and board manufacturing
- Performance specification for converters and printers
- Material selection for envelopes, maps, banknotes, labels and other fold‑intensive products
- Conservation and archival testing to assess durability of archival papers
- Independent testing laboratories and research into paper mechanics
Typical users: paper manufacturers, testing/quality labs, conservators, product engineers, procurement/specification writers.
Related standards
- ISO 186 - Sampling to determine average quality
- ISO 187 - Standard atmosphere for conditioning and testing
Annexes in ISO 5626 provide instrument descriptions (A), maintenance and calibration guidance (B) and informative notes (C).
