Food and beverage packaging continues to evolve as consumers want more options with their products. One of the constants amid the new packaging options is the use of hot melt adhesives for case and carton sealing. Hot melt packaging adhesives are designed to set quickly under short compression times to form strong bonds. To meet consumer demand, packaging lines need to run smoothly and avoid downtime. To achieve this efficiency, packaging line operators need to understand how the adhesive and equipment work together to create a great seal.
Hot melt adhesive systems are configured to meet the needs of each production line with an array of pumps, hoses, nozzles and tanks for adhesive application. From the melter tank, which heats the adhesive pellets or chubs, to the pumps which pressurize the molten adhesive, each component plays a role in the packaging process. A key component of the system is the hot melt tank pressure. Along with the nozzles and application temperature, it impacts the rate of flow and amount of the adhesive being dispensed. For each application, operators must:
- Determine the pressure setting
- Integrate set speed in the application
- Avoid adhesive build-up and overspray
Maintaining proper settings can avoid issues, which in turn can lead to downtime.
In the packaging industry, it is common to see tank pressures between 20 and 50 psi. If running too low, there may not be enough pressure to fire a clean bead onto the package. If running too high, the adhesive may fire too aggressively, hit the package and “splash” off. The hot melt adhesive tank pressure can impact the amount of adhesive applied. If not set to the proper level, the tank pressure can lead to further issues in packaging applications and impact production line efficiency. Typically, operators will increase pump pressure when:
- Adhesive beads are too small
- Adhesion issues arise or fiber tear is unsatisfactory
- Adhesive is not firing at all indicating a clogged nozzle
Although many operators may believe the easiest adjustment to solve these issues is to increase the hot melt tank pressure, there are some inherent downfalls associated with changing the pressure without completing a thorough diagnosis of the issue. Adjusting tank pressure increases the amount of adhesive being applied; however, pump pressure is not the only variable at play. Application temperature and nozzle size also work together with the pump pressure to influence application amount, which is one of the most critical components to package integrity. The following table shows an example of how an increase in pressure without any adjustments to the tank temperature or nozzle can impact the application amount.
An increase of 5 psi can potentially increase adhesive consumption by over 10 percent. While is it a small adjustment in pressure, increasing 5 psi can cost a manufacturer a significant sum over time. Beyond costs, there are some quality issues resulting from too high of an increase in tank pressure. If an adjustment to the tank pressure is needed, it should be adjusted in 3-5 psi increments.
% adhesive increase
% adhesive increase
% adhesive increase
Changing the hot melt adhesive system pressure can impact other areas of the packaging line. Set speed is often impacted the most when pressure changes are made. Defined as the time it takes for hot melt adhesive to become stronger than the substrate to produce fiber tear, set speed is a critical element due to its influence on hot melt pop opens. There is an inverse relationship between tank pressure and production line speed. If the tank pressure on the packaging line is increased, more adhesive is applied to the substrate which increases the amount of time needed for the adhesive to cool and adhere properly. This could result in slower line speeds to allow the adhesive time to set and create a good bond once compressed. Conversely, if the tank pressure on the packaging line is too low, less adhesive is applied. The production line may run faster; however, there could be pre-set issues if the hot melt adhesive cools off too quickly or there is not enough adhesive to make an effective bond between the two substrates.
Hot melt adhesives, like TECHNOMELT®, are dispensed by extruding a continuous stream of material. Increased tank pressure results in more adhesive applied to the substrate. This excess adhesive can cause overspray, which is a common application process challenge. In many cases the adhesive will fire or spray onto the production line. The increased pressure can also apply a greater amount of adhesive to the packaging substrate. This additional adhesive can squeeze out between the package’s flaps once it is sealed. This excessive adhesive could coat the belts or the machine, as well as affect the overall package appeal.
Understanding the hot melt equipment operational requirements helps identify and resolve process issues. Although, adjusting the tank pressure can sometime improve these issues, it is not always the answer to improve equipment operation. There are many variables which can impact the hot melt packaging adhesive application. The equipment manual is a good source of recommended settings. A general guideline for a tank pressure range is between 20 and 50 psi, as mentioned previously. When the hot melt tank pressure is operating above this range, there may be another issue such as clogged hoses or nozzles or char in the system. If excessive pressure is needed to overcome this blockage, it is recommended to thoroughly investigate your equipment and replace if necessary.
Understanding how to maintain operating consistency with hot melt packaging adhesive is important. Each equipment manufacturer has best practices to keep the machinery working efficiently and effectively. Food and beverage manufacturers rely on the effectiveness of hot melt packaging adhesives to assure a strong seal or bond. Brand owners need to understand the optimum adhesive performance to produce a secure bond.
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