Prediction of Score Cracking Propensity through Physical Testing

Fold cracking of linerboards is problematic in the converting process of box making. It is commonly exacerbated by the use of starch surface sizing, use of bleached kraft top liners or increased recycle content. It is desirable to have cracking preventable by selection of materials by testing prior to manufacture. This paper describes a series of tests that can predict fold cracking performance. The devised predictive tests are based on the principle that fold cracks are formed whenever surface fibers become strained beyond their yield points. Surface cracks, once formed, then propagate through the remainder of the cross section of the sheet. A modified tension test, and a modified Mullen burst test are configured to measure the yield strain in curved geometry thus preferentially straining the surface fibers. These new measurement techniques are shown to correlate with other more tedious fold crack testing such as the IPST crack angle test, MIT fold or AF&PA crack test and can be useful in linerboard production quality control.