What is the difference between ECT and ECV?

June 9, 2017

Charles asks,

What is the difference between ECT and ECV?

ECT (Edge Crush Test) is the testing method. ECV (Edge Crush Value) is the actual outcome or reported result of the Edge Crush Test. ECT is a measured in pounds per lineal inch of load bearing edge. Though it may sometimes be reported as ECV or lb/in it is typically reported or listed as an ECT value such as 23 ECT.

ETC has widely replaced the use of the Mullen test as ECT is considered by most as a more accurate test of the stacking strength of a corrugated box. It measures the edgewise compressive strength of a corrugated sample on an axis parallel to the sheet. Mullen, on the other hand, measures the bursting strength of the face of the corrugated sample, or on an axis perpendicular to the sheet.

– Ralph

 

Moisture Test Comparison MRA vs. non-MRA Box

May 24, 2017

Steve asks,

Would you have or could you please direct me towards any testing data/statistics on a box with MRA vs. a non-MRA box?  I would like to see what kind of improvement it shows in a moisture-related test.

The dimensions, flutes and composition range (very small to large boxes; B/C, E/B, and B flutes; 32ECT to 71ECT), and I don’t have much info on supply chain.  A customer just looking for any testing data that he can get on MRA to demonstrate that it does improve performance in moisture.

For assistance with answering this question I reached out to Clayton Clancy at Kruger. He has provided this this detailed study on stacking performance when using water-resistant adhesives, complied by the Institute of Paper Chemistry, which high-lights paperboard performance improvements when using WRA additives. He cautions that there are varying terminologies used when discussing water resistance such as (MRA, WRA and WPA), with that in mind I hope this will be helpful.

— Ralph

Cracking Litho-lam, Does ‘Sides’ Matter

May 8, 2017

Clint asks,

I have a question that I hope you can answer.  When using the same liner board on both the inside and outside of a singelwall sheet, why do you see more of the “flute lines” on one side versus the other?  What causes that and does it have more effect on fracturing the liners when you are creasing one side versus the other?

This came up when one of my customers was laminating a litho label on SInglewall.  They normally laminate it to the good side (less visible fluted lines).  Because some of the sheets were slightly warped, they laminated some on the bad side (more lines).  After converting there was some fracturing of the litho (not liners).   We saw less fracturing of the litho on the labels that were laminated to the bad side.  From a logical standpoint, if you put the label on the bad side and it is a weaker paper, I think the label may stretch easier versus being glued to a heavier liner.  Also, the inside of the box would look better (less visible flute lines) so I would assume this should be the norm unless you are just spot labeling something.  Keep in mind, the liners on the inner and outer were supposedly the same paper.

What are your thoughts on this?

 

Thank you for an excellent question. Yes, I can add some insight.

Tensile strength and stretch of the liners are impacted differently in the singleface and doubleback operations. Also temperatures and starch application are different in the two operations. Fracturing can occur in one liner and not the other. Learning flutes can have an impact. Microphotographs of the cross section of the combined sheet can begin to reveal some issues.

Of course starch application and amount can signal issues as you described. World class consumption would be about 1.4 # per msf.

– Ralph

Checking Starch Viscosity

May 4, 2017

Ralph asks,

Lately we have been having a debate about the perfect temperature for the starch viscosity testing. We use the stein-hall cup for our tests. Is there any specific temperature where it is best to test at?

Temperature certainly plays a major role in the viscosity of starch. Starch viscosity changes about 10% for every 2 degrees Fahrenheit. We discussed your question briefly with Herb Kohler of Kohler Coatings. Herb says that most corrugating plants that he is familiar with try to maintain temperature of starch in their storage tanks between 100 and 105°Fahrenheit (37.8-40.6°C). This helps maintain a steady viscosity and optimizes the running speed of the corrugator. Above 105°F (40.6°C) and you’ll start to experience viscosity growth. Maintaining a set point of 102°F (38.9°C) is commonly recommended by industry experts. His experience has been that is far better and more accurate to check the starch viscosity at approximately the same temperature each time than to rely on temperature/viscosity correction charts.

Additional information about regarding corrugator starch viscosity can be found in this Ask Ralph article from Roman Skuratowicz Ideal Starch Viscosity for Corrugated.

— Ralph