Inside Cracking on Singleface

November 24, 2021

Fern asks:

I am curious if there is anything written regarding inside cracking on the singleface liner and how it doesn’t take away from the structural aspects of the box, or if there is an industry guideline that I can refer to.

Of course we do our best to eliminate it all together, but now we are working with more & more recycled liners (some heavily recycled) and shorter fibers, we continue to battle this.

You are not alone in this struggle.  And it’s becoming that time of year when this becomes common for many cold weather converters.

One thing we need to remember is that recycled paper gives up moisture much faster than papers made with virgin fibers. When relative humidity drops below 50% the normal board moisture content can plummet leading to a more brittle liner. And, the short fibers of recycled paper create a structure that is more brittle to begin with than long fibre virgin.

Many converters use and/or have experimented with different score profiles and for virgin and recycled paper. The more aggressive, or sharper the profile the more likely to crack the liner. While 4pt crease may be typical, 6 or 8 point can be used to distribute the pressure across the surface.

AICC published a White Paper on Score Cracking a few years back. Click here to download the White Paper. The White paper is free to AICC Members.

We have visited this topic many times in Ask Ralph. Type “Cracking Scores” or “Cracking liners” in the “Search Ask Ralph” field on this blog.

— Ralph

EPA PBT Compliance Request

November 24, 2021

We recently received a request from a customer to sign a form/letter stating that we were compliant with the new EPA regulations on PBT’s in the boxes we manufacture for them. Have you heard of any other box maker that have been asked to sign such documents?

They also reference compliance to RoHS requirements.

Regarding the PBT compliance, probably the best and most efficient thing to do is contact your suppliers and request a reply, in writing, to the questions your customer has asked, and/or a COA (Certificate of Compliance) for both the EPA and RoHS regulations. You may be able to collect this information from their Safety Data Sheets, but make for you have the latest official documents from them, and if possible, make sure they are original documents and not photocopies.

The chemicals referenced in the January 2021 EPS issued rule include Decabromodiphenyl ether (DecaBDE), Phenol, isopropylated phosphate (3:1) – (PIP 3:1), 2,4,6-Tris(tert-butyl)phenol (2,4,6-TTBP), Hexachlorobutadiene (HCBD), and Pentachlorothiophenol (PTCP).

Typically we don’t think you’re going to find the chemicals in the EPA description in the paperboard, inks, or starch adhesives used to make standard corrugated packaging. We don’t know the exact extent of the information your customer is asking for, but if you are shipping product to your customer on plastic pallets, with plastic strapping, or plastic wrapping, you may want to request information from your suppliers of those products as well.

We have had a few discussions on RoHS compliance previously in this blog. In the sidebar under “Search Ask Ralph” type RoHS and hit enter to find these articles.

Do any of our readers and followers have any information or experiences to share on this topic?

— Ralph

Linerboard Coefficient of Friction (COF) Target and Max

February 3, 2021

Cassie asks,

I’m doing some investigation to determine what is the minimum, target and maximum COF (coefficient of friction) for linerboard. Can you point me to any information on this?

Instead of answering your question directly from a mill process point of view, which we can do, here are a couple links to several specification sheets from domestic mills. (Domestic High Performance Linerboard, COF Spec Sheets or Slide Angle)

The Europeans do not seem to deliniate slide angle as a physical property characteristic.  Since they have been making linerboard from recovered fibre much longer than we have in the Americas, it may be just universally understood there.

Let me know more if you have more specific questions. I would also recommend membership in TAPPI’s Corrugated Board Technical Committee where you will have access to the best minds in this business.


Stitching Tolerance

December 30, 2020

Dave asks,

 We have an old foot pedal stitcher we manually stitch boxes with. Is there a standard spacing between staples that we must maintain?

Dave, this was a new one for me.  Took a bit of research using a number of resources, but this should address your question.

Singlewall: Starting and ending staples shall be 1 to 1½ inches from the flap score lines.  Intermediate staples shall be spaced no more than 2½ inches apart.

Doublewall: Starting and ending staples shall be double stitched no more than 1 to 1½ inches from the flap score lines.  Intermediate staples shall be spaced no more than 2½ inches apart.  For products weighting 100 lbs. or more spacing of intermediate staples shall be reduced to 1 to 1½ inches apart.

Triplewall: Starting and ending staples shall be double stitched no more than 1 to 1½ inches from the flap score lines.  Intermediate staples shall be double stitched and spaced no more than 1 to 1½ inches apart.

— Ralph