ISO 11556:2005

Overview - ISO 11556:2005 (Paper and board - Determination of curl)

ISO 11556:2005 specifies a reproducible procedure for the determination of curl in paper and board using a single vertically suspended test piece. The standard defines key terms (curl magnitude, angle of curl axis, concave side), describes sampling and conditioning, prescribes test-piece sizes, required apparatus, measurement accuracy and the calculation of curl as the reciprocal radius of curvature (K, in m⁻¹). It is intended for cases where the curl approximates a circular arc and is stable during cutting and measurement.

Key topics and technical requirements

• Test pieces and sampling
  • Preferred shapes: circular (112.8 mm ± 0.1 mm diameter - area 100 cm²) or square (100 mm × 100 mm ± 0.1 mm).
  • Cut ten undamaged test pieces, keep consistent orientation and mark the machine direction on each piece.
  • Sampling guidance refers to ISO 186.
• Conditioning
  • Condition samples to a standard atmosphere per ISO 187 or measure “as received” rapidly to avoid transient changes.
  • Coated or gummed-label papers: allow at least 24 h stabilization after production before testing.
• Apparatus and measurement accuracy
  • Clean cutting device, test-piece support for vertical suspension, a modified engineer’s vernier calliper for chord (C) and chord-to-arc (h) distance (accuracy ±0.5 mm), and an angle-measuring device accurate to ±1°.
  • Annexes provide illustrations, support methods, calliper modifications, and alternate calculations.
• Procedure
  • Suspend test piece so curl axis is vertical, measure chord length (C) and chord-to-arc distance (h), identify concave side, record angle of curl axis relative to machine direction (clockwise + / counter-clockwise −).
  • Compute curl magnitude (reciprocal radius K) from C and h using the formula in clause 9.1; report individual results and statistics.
• Quality
  • Clauses on repeatability and reproducibility and required content of the test report.

Applications - who uses ISO 11556 and why

ISO 11556 is used by:

• Paper and board manufacturers for quality control and specification verification.
• Printers, converters and label producers to predict processability (feeding, registration, coating, printing, laminating).
• R&D and laboratory teams analyzing curl causes (moisture gradients, coatings, sizing).
• Buyers and suppliers to include objective curl criteria in contracts and acceptance testing.

Practical benefits include improved handling, reduced jam/registration problems in finishing and better product performance prediction.

Related standards

• ISO 186 - Sampling to determine average quality (referenced for consignment sampling)
• ISO 187 - Standard atmosphere for conditioning and testing

Keywords: ISO 11556:2005, curl measurement, paper and board, vertically suspended test piece, magnitude of curl, angle of curl axis, chord and chord-to-arc distance, modified vernier calliper.