Bending Measurement
Resistance of a paper or board sample to bending when it is clamped at one end and a force is applied to the other at a specific distance. This two point flexural stiffness is a fundamental property that determines how a carton will resist bulging and how it will perform on an automated filling line. The measurement provides data on the rigidity of the material, which is critical for both structural integrity and the tactile quality of the packaging.
Instrumental Procedure
Testing involves a precision instrument that records the force required to deflect the sample through a set angle, typically fifteen degrees. Results for two point flexural stiffness are highly dependent on the thickness of the board, as the stiffness increases with the cube of the caliper. This relationship means that even small variations in the manufacturing process can lead to measurable changes in the handling characteristics of the finished product.
Thickness is the primary variable.
Application in Converting
Cartons that are too flexible may fail to open correctly in high speed machines, while those that are too stiff might crack at the creases. Maintaining the correct two point flexural stiffness ensures that the package provides adequate protection for its contents while remaining easy for the consumer to use. This metric is a primary specification in the contract between the board mill and the packaging converter.
