Overview
ISO 5635:1978 specifies a laboratory method for measuring the dimensional change of paper after immersion in water. The standard defines how to soak conditioned paper strips, measure the change in length, and report results as a percentage relative to the original (conditioned) length. It is intended for use with most types of paper but is not suitable for sheets that become extremely fragile or curl excessively when soaked. ISO 5635 is distinct from standards addressing hygro‑expansivity.
Key topics and requirements
- Scope: Method for measuring dimensional change after immersion in water; not to be confused with hygro‑expansivity.
- Sampling and conditioning: Sample preparation per ISO 186; condition test pieces according to ISO 187 (standard atmosphere).
- Test pieces: Cut five specimens per test, each 250 mm long and 15 mm or 20 mm wide. The long dimension is aligned with the direction (machine or cross) under examination.
- Apparatus:
- Rigid test‑piece marker (~250 × 40 × 5 mm) with two chisel‑shaped metal pins set 200 ± 2 mm apart.
- Magnifying lens for measurement.
- Accurate graticule graduated to 0.2 mm.
- Procedure:
- Make two small slits 200 mm apart using the marker.
- Soak the specimen in distilled water at the conditioning temperature until no further length change occurs (15 minutes is usually sufficient).
- Carefully place the wet specimen on a flat surface, reposition the marker, cut a second slit, and measure the new distance between slits.
- Ensure specimens are not under any load while wet (wet paper is weak and can stretch under small loads).
- Expression of results:
- Change in length AL (mm) is converted to percent change: % change = 0.5 × AL (since the test length is 200 mm).
- Report the average of five results to the nearest 0.1%, along with test direction, conditioning atmosphere, soaking time and temperature, and any deviations.
- Precision: No repeatability/reproducibility data provided in this edition.
Applications and who uses it
- Quality control and material characterization in paper manufacturing, converting, and printing industries.
- Laboratory testing for specification compliance when water exposure or dimensional stability is a concern (e.g., packaging, labels, archival papers).
- R&D teams comparing formulations or coatings for dimensional stability after wetting.
- Standards bodies and testing laboratories that reference ISO test methods.
Related standards
- ISO 186 - Paper and board: Sampling for testing.
- ISO 187 - Paper and board: Conditioning of test samples.
- (Separate ISO standard on hygro‑expansivity is referenced as in preparation.)
Keywords: ISO 5635, dimensional change, paper testing, immersion in water, dimensional stability, water absorption test, paper standards.
