Overview
ISO 14968:2022 - "Paper and board - Cut-size office paper - Measurement of curl in a pack of sheets" defines a standardized test method to measure curl in cut-size office papers (typically those described in ISO 216). The method applies to sheets with maximum dimensions up to 300 mm and is used on packs of sheets (10–15 consecutive sheets). Measurements can be taken as-received, after conditioning, or after processing in a copier or other printing device to assess how curl affects office-sheet handling and printing performance.
Key topics and requirements
- Scope and sample size: Test packs consist of about 10–15 consecutive sheets; intended for uncoated cut-size office papers (60–150 g/m² range is typical).
- Curl definition and units: Curl magnitude is expressed as the reciprocal of the radius of curvature (units: reciprocal metres, m⁻¹). Curl also includes axis direction and concave side.
- Curl axis categories: Axis parallel to machine direction, perpendicular to machine direction, or diagonal (neither).
- Apparatus - curl gauge: A gauge comprising a 210 mm straight line and companion arcs (each at least 210 mm long) with arc radii chosen so curl magnitude varies between about 1.00 m⁻¹ and 10.00 m⁻¹ (Annex B provides construction guidance).
- Test atmosphere: Measurement can be done without standard conditioning (to capture as-removed or post-imaging curl) or in a standard atmosphere per ISO 187 when required.
- Procedure highlights: Measure curl on up to four edges (recommended), suspend the pack and match the free edge against the gauge arcs, record curl magnitude, axis direction, concave side and any double-curl tendency.
- Reporting and expression of results: If a dominant axis exists (parallel or perpendicular), report the mean of the two measured edges (m⁻¹); otherwise report all four edges. Test report must include sample identification, test atmosphere, imaging device details (if relevant) and all measured curl data.
- Precision: Within-ream repeatability observed in test data ranged approximately ±0.25 m⁻¹ to ±0.375 m⁻¹; inter-laboratory reproducibility data were not available in the draft.
Applications and users
- Quality control in paper mills and converting plants to monitor pack-level curl that affects downstream handling.
- Paper specification and acceptance testing for procurement teams.
- Reprographics and printer/copier manufacturers assessing how paper curl impacts feeding, jamming and duplex registration.
- Independent test laboratories and R&D groups investigating post-processing curl from imaging devices.
Related standards
- ISO 216 - Cut sizes (A and B series) and machine direction
- ISO 187 - Standard atmosphere for conditioning and testing
- ISO 186 - Sampling to determine average quality
- ISO 11556 - Measurement of curl in individual sheets
Keywords: ISO 14968:2022, measurement of curl, cut-size office paper, curl gauge, curl magnitude, machine direction, test method, ISO 216, ISO 187, ISO 186, pack of sheets, copier, printing device.
