Overview
ISO 16260:2025 - Paper and board - Determination of internal bond strength - specifies a standardized pendulum impact method to measure the energy required to rapidly delaminate a paper or board test piece in the Z (thickness) direction. The test quantifies internal bond strength as the average potential energy (J/m) absorbed during rapid splitting initiated by a defined pendulum mass and velocity. The method is suitable for single- and multi-ply papers and boards, including coated sheets and materials laminated with synthetic films, but is not suitable for samples that are structurally damaged by compression or porous enough to allow migration of adhesive.
Key topics and technical requirements
- Test principle: A square test piece is sandwiched between double-sided adhesive tape, fixed to a rigid metal anvil and an L‑shaped aluminium platen; a pendulum strikes the platen to initiate Z‑direction rupture. Energy absorbed is calculated from pendulum overswing and known instrument parameters.
- Apparatus: Pendulum with low‑friction spindle and defined striker, L‑shaped aluminium platen, metal anvil, test assembly preparation device (25.4 mm ±0.2 mm test area), and reliable latching/release mechanism.
- Specimen preparation: Use controlled pressure and time to adhere tape to both faces; ensure platen clamping to avoid flexing. Most preparation stations prepare multiple assemblies simultaneously.
- Conditioning and sampling: Follow standard atmosphere and sampling procedures (see ISO 187 and ISO 186 references) before testing.
- Calibration and verification: Mandatory instrument calibration and periodic verification (Annex A and new Annex B) to maintain measurement traceability; precision data and repeatability information provided (Annex C).
- Scope limitations: Not suitable for compressible or porous substrates where adhesive migrates; results from mechanical and electronic testers may differ (see Clause 12).
- Test reporting: Document instrument type, tester range, environmental conditions, mean value and standard deviation, and any deviations per Clause 13.
Practical applications and users
- Quality control and acceptance testing for paper and board manufacturers.
- Performance screening for converters and printers to predict susceptibility to Z‑direction impacts (picking, blistering, delamination) during printing and converting.
- R&D labs developing coatings, laminates, or multi‑ply products where interply adhesion is critical.
- Third‑party testing laboratories providing compliance and comparison data for suppliers and customers.
- Useful keyword contexts: ISO 16260, internal bond strength test, Z‑direction delamination, pendulum impact tester, paper testing standards.
Related standards
- ISO 186 - Paper and board: Sampling to determine average quality
- ISO 187 - Standard atmosphere for conditioning and testing
- EN 755‑2 - Aluminium and aluminium alloys - Mechanical properties (referenced for platen material)
ISO 16260:2025 provides a repeatable, impact‑rate sensitive method for assessing internal bond performance where rapid Z‑direction loads are relevant to end‑use quality and process robustness.