Ask Ralph
Expected Values for Containerboards Updated BY RALPH YOUNG
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n the last issue of BoxScore, we published news of a new greenfield recycled mill, with a sidebar noting the increased production and use of low basis weights or grammages. Included in the updated chart on the next page are some of these grades. In 2009, AICC conducted research with several members to determine different corrugators’ abilities to maximize the strength of the containerboards they were combining into corrugated boxes when measured by the edge crush test (ECT). What we discovered then followed early findings that corrugators differed by 25%–40% in their ability to efficiently convert the cross-direction ring crush of short column test strength properties of linerboard and medium into ECT. Corrugators today are more likely to have reduced that wide variation through better engineering and process controls and through more consistent containerboards. Modern converting equipment has also become gentler on the integrity of the corrugated structure, reducing the crush of the combined board and therefore lessening the reduction in the ECT value of the sheet. The findings were published in a 2009 BoxScore article. Contact me if you want a copy. To keep you somewhat current, we have updated the one-page spreadsheet that lists the strength levels in several grades of linerboard and medium. This testing is conducted on a semiannual basis through the American Forest and Paper Association (AF&PA). There is no breakout between kraft and recycled. Not all mills report. As AICC members, you have access to some information, and we can share the
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BOXSCORE March/April 2020
highlights with you. This chart is also tempered by various mill specification sheets that we are able to access on the internet. What you will find in the chart is a wide range of strength values within each substance or basis weight. Some of these variations can be more than 40%. So if you are still buying a grade by basis weight, that’s fine for Mullen boxes, but if you are into ECT and box compression, it is better to think along the lines of cost and strength. Important characteristics of medium that can impact obtainment of ECT strength are MD tensile, MD tear, and hot coefficient of friction as they relate to runnability. Attributes of linerboard that can impact the achievement of the maximum ECT strength are burst, coefficient of friction, slide angle, moisture, MD/CD
tensile, MD/CD tear, soft caliper, density, and porosity. The chart contains some values from the 2017 study only, because they were not available in 2009, so also check with your suppliers. New to this sheet is the inclusion of 18#, 21#, and 23# linerboards that were taken from other sources, because the AF&PA does not report on these grades yet. Ralph Young is the principal of Alternative Paper Solutions and is AICC’s technical advisor. Contact Ralph directly about technical issues that impact our industry at askralph@aiccbox.org.
