Tearing Glue Joints

October 31, 2014

Will asks;

We have recently had a slew of customer concerns in regards to glue joints. Our customers are saying that it is “tearing too easily.” This is for both hot melt and soft white glued boxes, (generally larger boxes that are NOT run through a flexo folder, but rather a Bahmuller or similar piece of equipment). Is there any way to baseline what poundage a glue joint should hold? Does it depend on what liner the board has and what material it is? If so how do you recommend measuring it?

Thank you for the question. First let me point you to an AICC resource, Key Characteristics of Linerboard and Medium and Their Impact on Combined Corrugated Board.  In that brochure you will learn what linerboard physical properties impact glue joint adhesion. Have you reviewed the FBA Handbook?  There is also a TAPPI Test Method for testing adhesives used in glue lap joints.

The strength of the glue bond is dependent on board moisture, relative humidity, slide angle, fibre type, surface strength and internal bond.

The type and location of the fibre tear, rather than an actual physical property value, will provide better information for identifying the source of the issue. Do you have any pictures to share? Is this a recycled linerboard?  Do you have any Dennison wax pick strips? Do you have containerboard mill specifications from the paper suppliers?

Where I am headed is that while it may be the adhesive, the environment, the process, the amount of coverage, it is usually a board and liner issue. Can you provide more information that will help us dig further into the issue?

Detecting Metal in Corrugated Boxes

October 29, 2014

Rich asks;

I have a food customer who must send product through a metal detector to ensure there is no metal in the food. Intermittently the detector has gone off and when they send my corrugated box through without product it still goes off leaving them to the conclusion that there is metal in the boxes. We are using recycled liners and the mill has essentially let us know that they cannot 100% guarantee that there will be no metal imbedded in the fibres of the box. The mill also provided me with a document from the FBA essentially saying that during the paper making process there is the slight possibility of small metal fibres getting into the paper. Is this consistent with how you understand it to be? Do we have any other options for guiding our customer and ensuring there will not be a chance of metal in the box? Is there a way to prescreen the boxes to determine which ones may have a trace of metal in them before I ship them? Is there a way to test the boxes to determine where the metal exactly is?

I must concur with the position of the FBA and the nature of the 140 domestic paper machines that manufacture containerboard. I have attended enough TAPPI CORBOTEC meetings over my 31 years to know that this concern comes up at every meeting three times a year.  Even the sophistication levels at the different recycled mills vary in their ability to remove metals from the recovered fibre.

The sensitivity levels of different detectors vary as well and the food industry is going to be using a very sensitive detector. Remember, they are looking for the tiniest pieces of metal in food. So a piece of metal that is likely to trip the detector they are using may not trip a more standard detector. You might have passed another packer’s inspection process depending on their equipment and sensitivity settings. The only sure way to prescreen your boxes to your customers’ spec may be to have the same metal detection system and sensitivity settings as your customer is using.

As far as pinpointing the location of the metal in the box, I do not currently know of a way to determine the exact location of the metal IN the board. I would think that this would require some type of probe detector that would be extremely sensitive and have a very narrow scan range. I would also believe the process would probably be quite time consuming and costly.

I don’t know how sensitive the wand type scanners that security firms use are. If you’ve traveled through an airport you’ll know that these can detect something as small as a staple in a paper… when they want too. If you could locate one of those it might be worth trying to see if it would pinpoint the offending contaminant. I wouldn’t suggest asking the TSA though. They don’t tend to have a sense of humor.

Another possible means for pinpointing the metal in the box or sheet would be x-ray. This too will most likely be expensive and time consuming.

However, from past experience if there is metal in your box, it will most likely be found in the medium.

— Ralph

ECT Litho-lam Vs. Corrugated

October 24, 2014

Bruce asked,

 Do you have any information on singleface lam vs. corrugate with regards to stacking strength? Also, if a corrugated box is in 44 ect what would we run in the litho world to come up with the same board combination?

Thanks for the question. Okay, here we go. This made me do some a few new searches, make some new network contacts, and dust off some old paper files.  Click here to download a file created with the CD ring crush values for coated white top linerboards, C1S offset label, and SBS.  The latter two were difficult to find since the “white” products are measured for Taber stiffness and not with the methods we use in the containerboard and corrugated industry.  I had to reach out to my contact at the Renewable Bioproducts Institute at Georgia Tech for a comparison.

Be careful about converting from double wall to singlewall. With the loss of spring back caliper in the board construction, one will lose bending stiffness, while ECT may be the same.  Both physical properties make up box compression and performance.  Have you considered B/E double wall with ultra lightweight components?  Kapstone makes these grades at Longview, and maybe Port Townsend also.

So to construct a minimum 40 ECT a corrugator needs to combine a minimum of 216# of CD ring crush in the three or five components. Corrugators vary in their ability to maximize the inherent strengths in the linerboards and medium from plus 15% to minus 25%.  Do you know your sheet feeder’s profile?  To achieve a minimum 44# ECT the suppliers need a minimum of 235# of CD ring crush.

Converters vary in their ability to maintain the incoming ECT by plus 0 to minus 35%. Have you benchmarked your presses, people and process?  The Chalmers DST is an excellent instrument to measure your degradations factors.

Under ideal circumstances, corrugators and converters can obtain a minimum 40 ECT B flute with 36/30/36 and a minimum 44# ECT B flute with a 36/36/36 or a 42/26/42 combination. I prefer to put more substance and strength into the medium.  30/23/26/23/30 will give you more than enough for 44# ECT.  Is this a cost effective alternative?  Usually we see a 5-85 fibre savings.

— Ralph

Litho-lam effect on ECT

October 9, 2014

Steve asks:

We are laminating an 80 lb label to an outside liner. The combination needs to equal 44ect. Can we lighten our board combination with the addition of the label?

If so, what would the combination be? We buy 44ect with the following 42 x 36 x 42. Any insight into this matter is much appreciated.

I will give you a ballpark answer to your question. However, we can get an answer with far greater accuracy if we know the combined ring crush value obtained when the top sheet is laminating to the outside liner. Would any of your sheet suppliers be willing to send some samples to their mill suppliers to obtain the laminated ring crush values?

To answer in general terms. Depending on the strength values of the components and the quality of the corrugator’s combining ability, the range in ECT across the industry before converting, would be 42-57 PLI. Do you know what you are being supplied today and how much you are degrading the sheet during the converting process? I would not change a thing until we have answers to the previous three questions.



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