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

White Linerboard Cracking at Score

March 24, 2017

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

German to US Board Equivalents

March 22, 2017

Luke asks,

Quite often, I receive requests to spec out a box that was originally designed in Europe– most often Germany or Belgium. I have had a really hard time finding US equivalents to some of the board combinations used “over there”, both in flute and paper weights. What we struggle with most is the board codes (e.g. PLK 140/ WS 115/ TL 140 or TLW135/WS70/TL135, ZNNW43).

Is there a resource out there somewhere that I can utilize to best determine a US analog for flute combo/paper weights?

To answer your question about your specific combination above it would be coated liner 29#/ waste based 23#/Testliner 29# and test liner white 28#/waste based 14#/test liner 28#. I have no idea of the ZNNW 43 name. However, take a look at these two documents. They may give you the information you need. Alternative Requirements Table, Transport Quality Requirements.


UN Testing – Can the same code be used for different suppliers?

February 23, 2017

Dana asks,

I have a few questions for you regarding UN testing. We have a customer who requires testing for their HazMat packaging. A few questions arose when we met with them recently. If you could offer your expert answer on the following, I would greatly appreciate it.

For one item they have 2 different bottle suppliers. If they include one bottle manufacturer’s specification, can they use a different manufacturer who follows the same specification? Or does the test need to be run for each different situation? If the test needs to be run for each different situation, how does the code on the box work? Can you have more than one code per box or would that one code be able to cover the 2 different bottle manufacturers?

If the customer uses 2 different caps on the same bottle, must each situation go through the test? Again, same question applies to the code on the box. Can they use the same box with 2 different cap situations?

The customer is using various different labels on the bottle. I believe this is okay as the labels vary slightly in thickness, but I do not recall seeing a material data sheet for the label when the prior testing was completed.

The customer uses different collars on the bottles. Does the collar need to be included in the testing and same questions apply here as the above cap and bottle situations?

I reached out to my associate Steve Brion at Ten-E Packaging Services for help with this question. Steve’s expert answers are below. — Ralph

“Yes, you can test one bottle manufacturer and use other bottle manufacturers as long as the product they supply follows the same specifications, or falls under Selective Testing Variation #1 in Title 49, CFR.

If your customers uses different types of closures on the bottles, then each closure variable combination must be tested and rate. Collars would also be treated the same as caps and closures. Each collar variable combination would need to be tested as a change in cap or collar design in essence changes the structure and/or specification of the container.

I haven’t dealt much with labels, but unless the label is structurally part of the bottle it shouldn’t make any difference for testing purposes.”