Unfortunately, there are a wide range of potential reasons for the failures. Without more specifics on the package type and content, it will be difficult to give you a solution, but I’ll give it a shot and hopefully head you in the right direction. Several factors could weigh in, but there is one piece of information that we can focus on and that is the center seal.

Since the package is only failing at the center seal, this signals that the seal is the weakest part of the current package. You do note that this is a center seal, but it isn’t clear whether this is a fin or lap seal or if the failure is happening along the back of the package or at the apex where the center seal and top or bottom seal meet. This apex is the one of the more difficult areas to seal on a standard pouch. If it is a fin seal, there are four layers to seal through and a difficult apex where the fin meets the end seal. For a lap seal, the apex is not as difficult, but can still cause problems as there are three layers to seal through.

In order to overcome this, good caulkability is required in the seal area. In other words, the sealant must soften, flow, and caulk the apex to ensure it is not a weak point in the package. The issue is how to get heat more efficiently from the jaws on the outside of the package to the sealant on the inside of the package. This can be overcome by longer dwell times during sealing (combine slower speeds with higher temperatures), increasing the seal jaw pressure, utilizing broader seal range resins in the sealant, and using polymers that are more elastic and stretch or elongate during the break.

Testing seals to achieve higher seal strengths over a broader range of sealing temperatures is key to determining the best structure. Once you have the seal profile in the lab, you will have an idea of the temperatures require to get the ultimate seal strength on the packaging machine. If you compare the lab test with seal tests off the packaging machine, you can quickly determine whether you are achieving the maximum seals possible or not. This will tell you whether the changes can be made on the packaging machine or whether the sealant needs to be modified. The sealant material can be modified as described above for a broader range sealant.  Also, a more elastic and tougher polymer can be used, or the thickness can be increased. Since this is a 40-micron sealant, moving toward a thicker sealant, say 60- or 70-micron, could provide more poly to flow and caulk the seal areas.

A secondary factor could be the package headspace.  If this is a dense product or especially a liquid and there is little headspace in the package, the weakest part of the package, in this case the center seal, will fail from the force of the content weight at impact.  This could be part of the problem.  Testing different fill volumes or package sizes to increase the headspace could identify this as a problem.

So, evaluate the seal profile of the laminate compared to the package to ensure maximum seal strength is being achieved. If needed, try adjusting temperature, pressure, and speed to achieve the maximum seal strength. If there are still failures, begin evaluating thicker sealants, broader seal range, and higher seal strength sealants.  Lastly, be sure to optimize the package headspace, keeping in mind that the package must still fit into the same size carton.  Best of luck!