Internal bond strength of paperboard (z-direction tensile)

This method describes a procedure for measuring the internal fiber bond strength (z-direction tensile strength) of paperboard using an instrument that separates a specimen adhered between a 6.45-cm2 (1-in.2) platen and a self-aligning platen.

The procedure consists of applying double (two-sided) coated, pressure-sensitive tape to both sides of a test specimen. The specimen is then placed between two platens and compressed uniformly over the entire specimen surface area. Uniform tension is then applied over the entire test area in a direction perpendicular to the plane of the sample (z-direction) to affect a separation.

The test is intended for paperboards and some papers which have internal fiber bond strength (cohesive strength) lower than the adhesive bond strength of the tape to the specimen and/or test platens. The material from which the platens are made will affect the adhesive strength between platen and tape. The selection of tape may also affect test results. These effects may be seen as tape failures or in some cases higher test values caused by adhesive migrating into sample. The adhesive bond strength of the tape is critical to reproducible test results. New batches of tape should be tested for consistent bond strength. Bond strength can be tested by performing peel tests on standard test plates, or by testing a stable reference sample.

Test results by this method do not correlate with TAPPI T 569 “Internal bond strength (Scott type)” measurements. TAPPI T 569 uses a pendulum that impacts the top inside surface of a platen at a high speed causing it to rotate and split the paper specimen.