Determination of tensile strength in the Z direction according to TAPPI T541 or ISO 15754

The tensile strength perpendicular to the material plane (internal bond strength) is a key quality characteristic for many paper-based materials. The Z-tensile test or internal bond test according to TAPPI T541 or ISO 15754 is used to determine the adhesive strength between the layers of a material, especially in multi-layer paper, cardboard or paperboard, as well as in fibre-bonded paper.

What is being tested?

In the internal bond test, the specimen is loaded perpendicular to the plane – i.e. exactly where different fibre layers or coatings are bonded. The test determines the force required to pull the layers apart until they break. This allows conclusions to be drawn about the material quality, the uniformity of production or the suitability for further processing.

The test procedure at a glance:

In the Z-tensile test, a defined specimen is bonded between two metal plates. After curing, it is pulled apart perpendicularly until the specimen fails. The force applied is a measure of the layer bond strength, which is a critical parameter for assessing layer adhesion in modern packaging and functional materials.

Typical areas of application for Z-tensile tests according to TAPPI T541 or ISO 15754:

• Packaging cardboard: Evaluation of internal strength, e.g. in transport packaging or folding boxes
• Graphic papers: Testing for delamination tendency in coated or laminated materials
• Corrugated board and composite papers: Checking the bond between the layers
• Tissue and hygiene papers: Quality assurance for multi-layer products
• Battery technology: Testing the adhesion of active compounds to aluminium or copper foils

Why internal bond tests are important:

Paper products are exposed to a wide range of stresses – whether during punching, folding, printing or climatic changes. Insufficient strength in the Z direction can lead to delamination, tears or functional failures. Testing in accordance with TAPPI T541 provides a reliable method for detecting such weaknesses at an early stage and improving product quality in a targeted manner.

Test system for determining Z-tensile strength according to TAPPI T541 or ISO 15754

A universal testing machine inspekt solo was used in a recent customer project to determine the tensile strength in the Z direction. In combination with a special test fixture, it ensures precise testing of the tensile strength perpendicular to the surface.

• inspekt solo 2.5 kN universal testing machine
  • High measuring accuracy
  • Compact workstation design with large machine base plate for storing accessories, tools and specimens
• Special test fixture optimally matched to internal bond tests according to TAPPI T541 or ISO 15754
  • Compatible with materials such as paper, cardboard, composite materials, functional films, coated anode and cathode films in lithium-ion batteries
  • High transverse rigidity ensures precise and repeatable test results
  • Time-saving and efficient test sequences by testing 5 individual specimens with only one specimen application
• LabMaster material testing software including standard-compliant test sequences and result display

Conclusion

The testing system offers a practical and standard-compliant solution for determining tensile strength in the Z direction – both for classic packaging materials and for modern materials in the energy sector.

Further information on the test system on request