Bending stiffness is an important property of paper and board, and perhaps the most important property of packaging boards. The majority of standards refer to 2-point methods for measuring bending resistance, of which many can be performed at Smithers Pira.
The stiffness of folding box board is measured using a Smithers Pira Board and Crease Stiffness Tester (CBT2). The 2-point bending stiffness of paper and paperboard can also be determined by Smithers Pira using Kenley, L&W and Taber instruments. The results are quoted in mN (bending resistance) or mNm (bending moment).
Smithers Pira is UKAS, ISO 17025 accredited for these test methods. The instruments we used satisfy the requirements of British Standard BS 3748 and International Standard ISO 2493.
Clarke stiffness measures the stiffness as the free length in centimetres of a paper strip which bends under its own weight. Clarke stiffness is measured in accordance with Tappi T451.
The resonance method works on the principle that the natural vibrating frequency of a material is related to its bending stiffness. Smithers Pira use an Adamel L'Homargy (Kodak Pathe) instrument to measure the resonance stiffness of paper in accordance with International Standard ISO 5629.
The Taber Stiffness, Clarke stiffness, and Resonance Stiffness testing methods are included in Smithers Pira's Paper Proficiency Service.