Bending stiffness and rigidity testing

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 Pira.

The stiffness of folding box board is measured using a Pira Board and Crease Stiffness Tester (CBT2). The 2-point bending stiffness of paper and paperboard can also be determined by Pira using Kenley, L&W and Taber instruments satisfying the requirements of British Standard BS 3748 and International Standard ISO 2493.

Pira is UKAS, ISO 17025 accredited for these test methods. The results are quoted in mN (bending resistance) or mNm (bending moment).

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. Pira use an Adamel L'Homargy (Kodak Pathe) instrument to measure the resonance stiffness of paper in accordance with International Standard ISO 5629.

The Clarke stiffness, Taber stiffness and resonance stiffness testing methods are included in Pira's Paper Proficiency Service.

Contact:

Doug Leatherdale
email: doug.leatherdale@pira-international.com
Tel: +44 1372 80 2108