Internal Bond Test/Z-Direction Tensile Test
In the internal bond test (Z-direction tensile test) the internal bond strength between layers is determined in accordance with TAPPI T 541 (or also ISO 15754). The bond strength between the layers of multi-layer materials (duplex or coated papers) is measured. This determines processability during printing or after coating. Loading according to TAPPI T 541 (or ISO 15754) is in the form of a force applied perpendicular to the surface of the specimen. To keep the testing equipment from influencing the separation of the layers, the force must continue to act vertically even if the specimen fails, for which high transverse stiffness and absolute parallelism of the specimen grips are primary prerequisites.
Internal Bond Test with ZwickRoell (Z-Direction Tensile Test)
- Specimen carriers arranged at 90° to each other enable 5 individual specimens to be tested in succession with a single application.
- The specimen carriers are mounted on precision compression plates and are accordingly parallel and stiff in the tensile and transverse directions. This ensures precise and repeatable test results.
- Specimen application: a specimen is attached to one specimen carrier using double-sided adhesive tape. Double-sided tape alone is applied to the opposing second carrier.
- During the test sequence the specimen is initially pressed against the second specimen carrier. Compressive force and duration are freely adjustable.
- The specimen is then separated in less than half a second in the tensile test.
- The measured quantity is the tensile strength, related to the surface area of the specimen, yielding the tensile stress.
- Pressing on specimen plus tensile test in one operation.
- Tests using half the test area are possible for high-strength specimens.
- The test device is available in both manual and semi-automatic versions. The semi-automatic version allows a second strip of specimens to be prepared while the first strip is being tested.
Comparison with the Scott Bond Test
The internal bond test offers greatly reduced result dispersion compared to the Scott bond test, which is used to determine similar paper properties. Other similar tests include ply-bond strength to DIN 54516 and the Scott bond test to TAPPI T 569, both of which apply peel loading to the specimen. A pendulum impact tester is used for the Scott bond test. The test therefore takes into account the high processing speeds typical for this material, but is considerably less reproducible due to internal energy losses through friction and vibration.
