Mike asks,
I have a customer that runs case make up units using a solid set hot melt. As of late we have an issue with the appearance of the seal on the bottom of the carton. When we are using light weight single ply liners the customer is not seeing fibre pull when breaking the bottom flaps apart to check for a bond. They are now considering this test to be a fail. Even though we can do a shake test and it passes. When pulling the cartons apart by hand the strength feels the same if you have fibre pull or not. When we are not seeing fibre pull what you see is the hot melt glue lines on each flap that is stuck to the paper so it looks like the glue came apart in the middle.
Anyway, is there is a tool that we can measure the bond strength on the bottom of a carton?
If glue is remaining on both flaps and is not separating from the paperboard, then the bond between the paperboard and the glue would appear to be good. If we take a lesson from the corrugator, too much glue can be as bad as too little glue. Too much and you risk shear within the glue itself. I’m not positive if the same ‘holds’ true (pun intended) in hot melt. I know too much hot melt can cause a variety of problems, but I’m not sure if shear within the glue is one of them. I’ve reached out to some of my industry contacts and I’m awaiting their input. I’ll update this post as when received.
I’m not sure if here is an official measuring device. However, I would think that if the box was to hold, say 25 pounds, you could get 25 pounds of weights at the local sporting goods store, place them in the bottom of the box and then somehow suspend the box so the full weight was on the bottom flaps. Perhaps do a few jerk tests where you would quickly lift the box with the weights in it. This would simulate the additional forces of acceleration. If it supports the weight, perhaps your customer would accept this as proof that the bond is sufficient to hold the prescribed weight. Be careful when you are testing.
Okay readers, has anyone else seen this type of separation with hot melt? Do you have any experience or suggestions to pass along?
— Ralph
askralph 
December 1, 2017 at 5:14 pm
According to Pierce Covert of Glue Machinery Corporation, inconsistent compression can cause this type of hot melt separation. He also adds the type of glue and the application temperature can also contribute to separations of this type. Thank you Pierce.
I know this doesn’t answer your original question about testing, but perhaps it will provide some direction into finding the source of the problem.
— Ralph
December 7, 2017 at 5:40 pm
Ralph,
This is not a board problem. If the glue splits, with glue remaining on both surfaces, it is a glue problem or an application problem. In so far as measurement is concerned, other than your suggested method (a good one), the glued joint can be peeled using a tensile tester. We test glue joints this way from time to time. It should be understood that the measurement will be affected by the area of contact and if there is fiber tear the internal bond of the surfaces being glued affects the test results.
Vann Parker
Applied Paper Technology, Inc. 1935 Delk Industrial Boulevard, Suite B Marietta, GA 30067
678-627-0222 x22
http://www.appliedpapertech.com