1.1 This test method covers a procedure used to measure the resistance to bending of paper and paperboard.
1.2 This test method is used to determine the bending moment required to deflect the free end of a 38 mm (1.5 in.) wide vertically clamped specimen 15° from its center line when the load is applied 50 mm (1.97 in.) away from the clamp. The resistance to bending is calculated from the bending moment.
1.3 TAPPI T 566 “Bending Resistance (Stiffness) of Paper (Taber-Type Tester in 0 to 10 Taber Stiffness Unit Configuration)” describes a modification of the instrument described in this test method for measurements in the 0 to 10 Taber stiffness range only, and which requires a smaller test specimen. The modified procedure may be recommended for papers which are low in grammage, highly flexible, or both.
1.4 Test results obtained using modifications of the basic Taber-type instrument such as that described in TAPPI T 566 “Bending Resistance (Stiffness) of Paper (Taber-Type Tester in 0 to 10 Taber Stiffness Unit Configuration)” have been reported to be as much as 40% different from those obtained using this test method, and such modifications must not be used when this test method is specified.
1.5 Other procedures for measuring bending resistance include TAPPI T 535 “Bending Stiffness of Paper and Paperboard (Resonance Length Method)”; TAPPI T 543 “Bending Resistance of Paper (Gurley-Type Tester); TAPPI T 556 “Bending Resistance of Paper and Paperboard by Single-Point Bending Method”; and TAPPI T 836 “Bending Stiffness, Four Point Method.” TAPPI T 535 has been classified as Classical.