Archive for the ‘Finishing/Converting’ Category

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

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

Insulating Properties of Corrugated

August 15, 2019

Rich asks,

I have a question about the insulating properties of corrugated and the impact of vent holes in dairy applications. I have a dairy customer who is looking to pack sour cream in cartons. It is filled at 100 degrees F and put into 35 degree refrigeration. What is the difference in how long it will take to get down to 40 degrees if there are no vent or hand holes in an RSC against if there are some? Is there a formula that exists for the cooling time? This would be an ECT48 DW RSC. Thank you as always for your guidance.

Here is a link to a research paper (Overall Effective Thermal Resistance of Corrugated Fiberboard Containers) complied by the US Dept. of Agriculture and the Forest Products Laboratory. Pages 4 – 6 of this report contain information regarding the affect of vent holes.

The location and area of the vent holes as well as the velocity of the circulating air will also have an affect on the thermal transition time.

Would it be possible to perform an experiment using a grill or meat type thermometer to determine when the core of a loaded box with vents and a loaded box without vents reached the desired 40 degrees F?

— Ralph

Measuring Force to Break PDQ Perforation

April 10, 2019

Pete asks,

We have been working with several different perf styles to provide ease of opening for retail ready PDQ style trays. There is a variety of different sizes and the majority of the items are earmarked for Walmart stores. While our execution has been successful we do not have an effective process to measure the force required to open the boxes to ensure consistency. Are there any tests to can recommend or any laboratories capable of testing the variables we are trying to measure?

Very good question Pete! You might review TAPPI T-813 which discusses the tensile test for the manufacturer’s joint. There are also jigs for compression testers that will measure the force necessary to bend a crease through a certain distance, usually to a 90 degree angle.  Also check TAPPI 577 and 829 for ideas.

Another option may be to use a burst test at the point of the perf. TAPPI T-810 describes the burst testing method. The question would be whether conventional equipment would have a satisfactory range of operation/measure or would the bursting strength of the perforation be below the recommended operating range of the equipment.

Now let’s toss this one out to our readers to see what their thoughts and experience may be. Has anyone done this type of testing, or is anyone aware of a specific method for testing the force necessary to break a perf?

– Ralph