Ideal Starch Viscosity for Corrugated

June 30, 2016

Khuram asks,

I have a few queries regarding corrugated glue.

  • What should be the ideal viscosity and %age solids range for corrugated glue adhesive?
  • Which one is the standard cup to measure viscosity of corrugated glue?
  • As viscosity changes with temperature so can you provide any graph showing change in viscosity of corrugated glue with temperature?
  • As in summer season temperature is higher so viscosity will be less. Is it advisable to control viscosity by adding borax in summer season?

 

We reached out to Roman Skuratowicz at Ingredion for some expert insight to Khuram’s question. Here’s Roman’s response.

  • Ideal viscosity varies by machine, BHS typically likes 40-50s Stein Hall viscosity, others may like something between 30-40. Most machines overall will run between 30-60 seconds Stein Hall. Fresh adhesive is better than storage adhesive. Using adhesive within hours is preferred but if needed adhesive can be stored overnight or for days with proper formulation, agitation and temperature control.
  • The Stein Hall cup is the standard measure for starch viscosity, although there are European versions as well as the US version. I have only ever worked with the US version, which can be purchased from https://www.gardco.com/pages/viscosity/vi/steinhall_cup.cfm  or  http://www.ringwoodstarchmix.com/ among other places.
  • Correct, viscosity changes with temperature. Follow this link for a temperature/viscosity reference table “Temperature – Viscosity Correction Table (For Stein Hall Viscosity)”. This table is approximate but provides a good guide.
  • First adjustment for viscosity is typically to add or remove a few pounds of starch in the primary. Adjusting borax changes the chemistry of the adhesive and does not impact viscosity as effectively as primary starch. You can also adjust shear time in the primary or borax mix which will impact viscosity. That said, reducing water temperatures is important as you want to keep adhesive storage temperature below 105F, otherwise you will see viscosity growth in storage. Controlling temperatures on the corrugator is also important, as high paper temperatures will flash water from the adhesive and result in brittle, crystallized bonds.

Revisiting Metal Detection in Paper – updated

June 30, 2016

Mario asks –

I read your post on ASK RAPLH about detecting metal in corrugated. Did you find some solution to detect metals in the corrugated plants? We have had issues that have damaged relationships with some of our customers in the food industry.

I would appreciate your comments.

Update – Click here or scroll down

I just returned from my summer meeting with my technical peers that are members of TAPPI. This was one of the subjects we discussed.

One paper mill system with three 100% recycled fibre machines runs samples from every fourth reel, but has never detected metal from its scanners.

You will need to buy a scanner the same as your customer. You will need to calibrate it according to their sensitivity levels. Make sure you can track the order from the receiving of the sheets from sheet supplier, through your converting equipment/process and all the way to delivery of the finished product to your customers. Once you find the source of the metal and your sheet supplier. Once you identify the source of the metal contamination, then you can address the issue.

If you haven’t read the comments from Bill and Clayton regarding detecting metal please click on this link and scroll down the page. Both gentlemen offer some very good insight based on in-plant experience.

Check with your customer to see what kind of detection system they are using and if the same or similar system may be available to meet your needs.

Update
Dick Lund – RC Lund Consulting.

Metal in paper is usually from virgin paper mills – sloughing off of metal in the machines or poorer fiber cleaning than is used in recycled mills.  Recycled mills are specifically designed to remove metal and other contaminents, virgin – not as well equipped.  Further, testing boxes on line in a box plant may be possible but it is very expense and difficult to execute.  Better to get metal free paper!

 

Cracking Score on White Liner – update

June 27, 2016

Kaleb asks,

We are facing cracking issue in our white test liner when it is used in a particular material combination. Pictures are attached for your reference.

Kindly provide your expert opinion.

 

 Cracked Score 3 Cracked Score 2 Cracked Score 1

Allow me to make a few observations and ask a few questions that may help us find an answer to your question. Since this is double wall corrugated I assume this was converted on a rotary diecutter and not on a flat bed diecutter.

When was the last time you changed out the slotting knives and scoring heads?

Do you change scoring heads and profiles between single wall and double wall?

What was the relative humidity and board moisture at the time of converting?

It appears that the white top did not have enough tensile strength and elongation potential to survive the folding. What does the mill have as far as retained physical property tests and samples for the top sheet that you combined and converted?

Can you supply the scoring head profile so that I can review the design with some of my domestic associates?

–Ralph


Here’s an update on Kaleb’s cracking issue. After some back and forth discussion we’re still looking at Kaleb’s problem.

He has provided the following additional information on his issue.

The box is being die-cut on a rotary diecutter.

  • They change the slotting knives and scoring heads on a weekly basis, but they do not change between singlewall and doublewall orders.
  • Relative humidity of conversion area was about 45-55% and moisture of board was 7-8%.
  • Average Tensile strength and elongation values of top liner are as following:
    • Tensile Strength MD: 7.6KN/m
    • Tensile Strength CD: 5.0KN/m
    • %age Elongation MD: 2.5%
    • %age Elongation CD: 5.5%

Rick Putch of National Steel Rule provided this info…

Pre-crushing before slotting can help reduce score cracking. Also, closing the slotter head nip a little tighter than normal may create additional crush. This can reduce stretch of the outer liner when folding at 180 degrees. I would suggest asking him to run at significantly different speeds to see if that has any influences on the cracking. Also ask Kaleb to put a dial indicator on score heads to see if they are concentric. If they are running out they may not be consistently crushing the score. Have him try these things and report his findings back to us.

How does his tensile and elongation numbers compare to US kraft liner?

These elongation values should be good for any liner.

Tensile values depend on basis weights which he not provided. For example 7.6 KN/m MD tensile stiffness would be typical for DS Smith’s 150g Eurotest, their 130g Testliner 3, less than 100g SCA kraftliner, and their 100g Eurokraft.

Please feel free to share your knowledge and experience. We look forward to hearing from our readers!

—Ralph

Scoring Allowance for Doublewall

June 7, 2016

Luke asks,

What should the scoring allowances be for an RSC in 350 AB flute? Thanks so much.  This is stumping me!

I reached out to Rick Putch of National Steel Rule for assistance on an answer to your question. Below is his response. Thank you Rick.

“As you can imagine basis weight matters, but below is what I used for BC:

If your B-flute caliper is .144” (with no facings) and A is .165”-.175”, I’d recommend going 1/16” more than your BC of same basis weight.”

DBLwall score chart - Scoring Allowance for DBL Wall

 


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