Glue vs Staples

September 9, 2020

Andrew asks,

Glue joints vs. stitch joints. What are the benefits of each type of manufacturing joint and which is stronger? Often I am told glue joints are stronger because glue penetrates and bonds the liners. Are there any test results that support this?

The intended use and environment that the container is going to be used in are key factors in selecting glue or staples for your manufacturer’s joint. For the majority of uses, glue is the preferred method because it provides a higher strength in most cases. Glues also enhances productivity because, in the case of a flexo folder-gluer, you can print, fold, glue and stack or bundle in a single operation while stapling would require a second operation. In applications where gluing is a second operation, it can typically be accomplished at production speeds far greater than stapling.

So why use staples? Well, they still have their purpose. Staples are often preferable for containers that are subject to high levels of moisture or exposure to outdoor elements and temperature change. These types of containers are typically coated with materials that repel water such as wax and other weather resistant coatings. Glue usually does a poor job of bonding these types of materials.

Both methods have their disadvantages too. As mentioned above, glued joints can be more susceptible temperature and moisture changes and may not adhere well to some printed or coated surfaces. Glued joints take a little longer to set, but since they are going through a stacking to compression device that’s usually a non-issue.

Staples may have a few more disadvantages. They are typically not desirable for use with food products and can complicate the recycling process. Staples can also scratch or damage products inside of the container, though this is more likely in manual than automatic operations. They can also create a bit more of a safety risk especially if they are not properly installed.

Here are some documents that provide additional information.

— Ralph

Roll Hardness Testing

June 12, 2020

Chris asks,

I was recently appointment QA manager at my company and have dove head first into the realm of Schmidt Hammer(roll hardness) testing.  A very significant issue we have is with warp.  I have noticed that most of the time when I see a difference of greater than 10 on the Schmidt Hammer test we suffer from unacceptable warp issues.   Since I’ve started hardness testing inbound rolls we have adopted a pass fail system where any roll that tests to greater than 10 is rejected.  To add to this problem our supplier has adhered to a system that says anything under 15 is acceptable by industry standards.

What is your take on this?  Do you feel that it is unreasonable to ask the mill to commit to less than a 10 difference?

Also, the mill is questioning my testing methods.  TAPPI T834 suggests to sample a roll every 6 inches across the roll (the mill uses this sample frequency).  I have always been taught that as for a scientific process that the larger sample size yields more accurate result.  With this being said, I chose to test my rolls at a frequency of every 3 inches which would increase my sample size.

Do you feel that my testing method is in some way negatively affecting the results?  As in, is my sample size causing the rolls to “fail” on a more frequent basis?

 

I love the three inch method. However, you would not be able to correlate to any of the 140 +\- containerboard machine out there. I would agree you are more likely to find a wet streak with your protocol, but mill specs usually call for moisture deviation to be six inches or less.

Do you have linerboard specification sheets from other companies?  You may want to investigate roll hardness from other manufactures. If your supplier is so entrenched in their thinking you might consider saving their rolls and having one of their Corrugator supervisors show you how to run the board without warp. It’s a bold move!

 

— Ralph

Acceptable Reject Rates for Corrugated Packaging

March 19, 2020

Ed asks,

I wanted to run something by you and see if you could point me in the right direction.

We have a client who orders a lot of different sized RSC’s in quantities of 2500. At one point we were having some issues with gluing and had to re-glue the boxes. However, we addressed the issue and it seems to have fixed the problem. But now every time this customer finds a box that isn’t glued properly he expects us to re-glue it. I am not sure if we should be expecting every box to be perfect, or if we are shipping them some bad boxes but not billing them for it.

Do you have any information on acceptable “non-conforming” box rates? Is there an industry standard for this?

TAPPI’s Waste and Productivity Survey provides a lot of valuable information, but I saw nothing  specific to glue tab or manufacture’s joint failures.

I talked with Ken Robinson at Baumer hhs. Here are com points to consider.

  • If you have a contact system you will probably always have an issue.
  • Two percent failures are to be expected.
  • Pre-cleaning the glue tab before it hits the gluing station helps.
  • Operator training should be constant.
  • An inspection system can reduce the reject rate to 0.1%.

If there is not a published industry standard reject rate then it most likely will fall back on the contract/agreement between the boxmaker and the customer. Does your contract address percentage of rejects?

Customers, especially those running or supplying automated packing lines may be looking for zero defects. Of course every boxmaker strives to deliver the highest quality with minimum rejects at the most competitive price. However, there is a cost associated with ensuring the delivery of zero defect loads. Is the customer(s) willing to pay that price? They too are looking for the best, most competitive prices. However, if the cost of ensuring zero defects is less than the cost of lost productivity and products, then they may be.

— Ralph

Corrugated Performance In Sub-Zero Temps

March 16, 2020

Jeff asks,

I have a client who is asking for specific information about corrugated performance at low temperatures (-20 degrees Celsius) for extended periods of time (up to 6 months).  I have not been given specific information about the contents of the boxes, but I suspect it to be clinical trial materials or something similar.  I expect them to be looking for some sort of performance guarantee.  Current board grade is 32 ECT C Flute.  Outside liner would be virgin paper.  The remainder of the box (medium and inside liner) is recycled paper.

Anything you can provide to help me with this?  Or can you direct me to the right place?  Thanks in advance for any help you can offer.

There just is not much out there, but here are a few things that we do know. Cold temperatures can cause strength degradation in corrugated packaging and other corrugated paperboard products. Moisture introduced from the repeated opening and closing of refrigerated units can also affect the strength of the corrugated container. Aqueous and UV coatings will certainly provide extended resistance to moisture on the boxes’ surface. However, what generally happens is the glue line is attacked by changes in atmospheric conditions. This is where we often see failure to the board itself.

Manufacture’s joints and/or flaps that are glued can also be subject to strength degradation at low temperatures. The same problem may be seen in boxes sealed with tape as the adhesives can become less tacky. There are tapes and glues that are marketed to offer better performances in both extreme low and high temperatures. While they may not help with the overall strength of the box, they contribute to the overall survivability and protection of the enclosed content.

Here is a link to the last industry wide study on freezer storage that we are aware of. It’s a bit over 70 years old, but still relevant. Note the added box strengths in the chart.

I’ll also include this link to the most recent report from the PMMI on the storage of Corrugated Packaging.

Does any of our other followers have any knowledge they care to share on their experience with long term or short term low temperature storage of products protected by corrugated containers?

— Ralph