White Linerboard Cracking at Score

Dana asks,

Regarding cracking on white liners, is there one specific liner type that will fare better than another?  Considering Kemi, Bleached White and Mottled White liners which is likely to provide the best performance and quality for rotary die-cutting with a perforation pattern of 3/8″ x 3/8″ perf-score or 1/2″ x 1/2″ perf-score.

In my experience, we have compared Mullen grades to ECT grades and understand the longer fibers to fare better than shorter fibers, but I have never before been asked this question in regards to the specific liner board color. I am curious to know if you have any data or experience related to this.

Kemi is extremely uniform and well-formed of virgin Northern European short hardwood fibres. Bleached white from the US South will be different than Canadian bleached. There is no more mottled white.  White tops can be composed of virgin or recycled fibres or a combination of both.  These are also made in the US South and Canada.

I would invest in a small microscope that you can connect to a laptop and look at the cross sections of both good and bad scores to see what is happening to the medium in both situations.  You might also consider sending samples back to your sheet feeder for flat crush testing. You may need a different medium.

Do you have the right rule and rubbering for the dies?  What does the supplier say?  If they do not know I will recommend an expert to you. Also, are your dies in good condition with no damaged rule or rubber? And don’t forget your anvil covers/blankets. Are they in good condition and do they have an even surface? It’s important that they are rotated, ground or trimmed frequently to maintain the proper anvil surface.

Cracking during the winter is often a matter of low moisture.  What combined board moisture do you have at the time of converting.  Do you know the individual containerboard temperatures at the time of combining on the corrugator?  It’s possible your supplier is ‘cooking’ the sheet on the corrugator causing it to become more brittle than desired.  Consider a Denver Moisture Analyzer somewhere in your system?  You need at least 7% moisture to have any success at scoring properly.

How is the maintenance on your presses?  Do you experience cracking more on one diecutter than another? Are there differentials between shifts?

Let me know how your investigation proceeds. I would be very interested in what you discover.

— Ralph

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