Of the many challenges that packaging managers face, perhaps the most ironic is the poor performance of high quality hot melt adhesives. Products that fail to bond on the packaging line, or pop open on the supermarket shelf in spite of a high-end adhesive having been used, are just a part of that story. Frequent line stoppages, excessive consumption of expensive adhesive and unnecessarily high human resource costs add to the inefficiencies that we seem to take for granted. An understanding of the root cause of these problems allows us to prescribe appropriate solutions and truly benefit from these modern adhesives. These are solutions that are available today, thanks to the rapid strides that state-of-the-art adhesive application equipment have made in recent years.
If you have run a packaging line that uses hot melt adhesive (HMA), you have faced situations where the product fails to bond at the end of the line, or fails to remain bonded till the consumer opens it. Whether it’s a cartoning line, a case erector, a top-and-bottom case sealer, or another adhesive application in packaging, this problem is common. Equally common are two responses: (a) increase the quantity of adhesive per product, (b) raise the temperature setting. Sadly, these are at best temporary solutions. Often, they are the wrong solutions. They simply do not address the likely root causes of the failure.
We will discuss here two possible causes for this that are most commonly encountered:
1. Inadequate or missing adhesive beads: A common problem in packaging lines, this is more often than not, caused by blocked nozzles, which in turn are triggered by the contamination in the system.
2. Low temperature adhesive: This can occur in spite of the temperature having been correctly set. HMA that is at too low a temperature has inadequate tack and this results in its inability to bond the substrates.
The problem of blocked nozzles is so widespread, it is almost an epidemic. People have accepted this problem as inevitable, and have devised many work-arounds. The fact is, blocked nozzles are not inevitable. This problem can and should be eliminated. The solution lies in first understanding that nozzles get blocked by particles that are not a part of the nozzle. They could have entered the hot melt system from the outside – typically dirt or dust from the environment. Or they could have been generated inside the system, as when the HMA gets charred and produces solid particles. Either way, you have a hot melt system that is dirty and contaminated.
So, you have external contamination and internal contamination that can cause a nozzle to block. Once these are recognized as the root causes of nozzle blockage, it is possible to devise countermeasures.
Next, one needs to address the issue of the adhesive temperature being too low. What causes this? For the purposes of this article, let’s discount the problem of the temperature having been set too low. This is a trivial problem, with a simple solution. The less frequently understood problem is a phenomenon called thermal shock. Briefly, this problem occurs when a HMA tank has been allowed to become almost empty, before being refilled with solid adhesive. The result is a sudden drop in the temperature of the adhesive in the tank and hence a drop in the temperature of the adhesive as applied on the substrate.
So we are dealing here with two common root causes: (a) contamination of the melt system and (b) the tank being refilled too late. Both problems are addressed by the current generation of tankless melt systems such as Nordson’s industry leading ProBlue Liberty™. This is a self-contained product that integrates melt-on-demand tankless technology with an automatic fill system. Unlike conventional melters, the Liberty does not have a tank at all. It has a small, high-efficiency melt grid that receives solid HMA, on demand, from an automatic fill system. It then heats the HMA rapidly and produces molten HMA at the required application temperature. A pump then supplies the molten HMA through heated hoses and applicators to the point of application. Because the adhesive is melted on-demand, it is held at the elevated application temperature for a very short period. Consequently, the possibility of adhesive charring (a prime cause of blocked nozzles) is virtually eliminated.
In addition, the automatic fill system does away with the manual intervention of periodically opening the tank lid for refilling. In conventional systems, this manual refilling operation is often extremely messy, and causes external contamination to find its way into the tank. Tankless melters, on the other hand, come with storage containers that can hold enough adhesive for several days’ consumption. In the case of the Liberty, for instance, the storage containers can hold up to 240 litres of solid adhesive. The system can therefore be left alone for several days, with no manual intervention for tank filling. There is no adhesive spillage, and no possibility of contaminant entering the system from outside.
Interestingly, the benefits of using the Liberty go beyond this.
Additional benefits are:
- Lower labour cost.
- Reduced adhesive spillage loss.
- Fewer broken lids due to over-filling.
- Cleaner operation of the system and hence the need for less frequent maintenance.
- A safer operation due to minimized possibility of contact with hot surfaces.
Tankless melt systems such as the Nordson ProBlue Liberty are setting new standards in optimizing packaging operations, minimizing loss and reducing cost. By eliminating the root causes of some of the most common problems, these systems allow the user to run an efficient, trouble-free packaging operation that consistently produces high quality packaged products for the modern consumer.
Suprotik Das
Managing Director, Nordson India Pvt. Ltd.