There is a lot of planning and design involved in consumer products. From protecting the contents to appealing designs to attract buyers, food and beverage companies can use hot melt adhesives to create a secure packaging. Hot melt packaging adhesives are designed to set quickly under short compression times, enabling strong bonds within seconds to protect the package contents. For packaging production lines to run smoothly and avoid downtime, operators need to understand how the adhesive and equipment work together to create a great bond.
Dispensing hot melt adhesive requires precision to assure the application is consistent under rapid production speeds. No matter the application pattern – dots, stitched beads or solid beads – it is important the hot melt adhesive nozzle provides clean cutoff, accurate placement and consistent material deposition. A key component of the application setup is the size of the nozzle. The selection of the nozzle size on an applicator plays a major role in the rate of flow and the amount of adhesive being dispensed or fired onto a package. Nozzles can vary by orifice size (diameter of the opening), or engagement length. Typically, nozzles are selected by their orifice size as it plays the larger role in affecting the adhesive bead width. For each application, the following must be considered when selecting the correct nozzle size:
- Achieving ideal adhesive bead width for package size
- Integrating set speed in the application
- Avoiding adhesive build-up from squeeze out or overspray
- Assuring good equipment condition
- Maintaining adhesive product levels and consistent temperature
Selecting the smallest orifice size that will not clog – generally ranging between 30mm to 45mm (0.012 inches – 0.018 inches) – is recommended to achieve optimal application.
Application temperature and tank pressure work together with the nozzle size to influence application amount, which is one of the most critical components to package integrity. A change in nozzle size can significantly impact the amount of hot melt adhesive applied. Typically, an operator’s first instinct is to simply increase the tank pressure when a nozzle is not dispensing correctly. Although this applies more adhesive and can help temporarily resolve some issues. Unfortunately, there are many other reasons a nozzle may perform inadequately. Some common reasons are:
- Incorrectly sized nozzle orifice for the application
- Obstruction at the nozzle tip
- Build-up around the nozzle head
Inconsistent adhesive application amounts could result in issues with the bond. It is important to keep the same size nozzles on the production line. This is critical for package integrity. If for some reason the nozzle size in changed, then all nozzles should be changed on the application and the tank pressure reduced or decreased to achieve an appropriate amount of adhesive. There are three simple steps to checking the nozzle performance.
Depending on the speed of a production line, nozzles may need frequent replacement. It is recommended to inspect nozzles weekly to check for clogs and replace every 4 to 6 weeks to keep the line running smoothly. It is critical to maintain the nozzle inventory to prevent different orifice sizes being used on the same application. If the wrong sized nozzles are used for replacement, it can lead to inconsistencies in the application amounts and potentially cause pop opens due to poor adhesion. If nozzle clogs are a reoccurring issue, it is not recommended to keep replacing or switch to larger orifice. Instead, an equipment or adhesive representative should be contacted for further investigation. A full system cleaning may need to be completed to remove any existing char and debris.
There are instances where a larger orifice is warranted. If a larger surface area is being adhered, then the operator should consider increasing the nozzle size. This may be the most efficient way to keep the line running. Although it is easier, there are some downfalls associated with just increasing the nozzle size. Switching to a larger nozzle orifice has a significant impact on adhesive amounts being applied. The following table gives an indication of this effect from a common industry example.
0.014" or 0.36 mm
0.016" or 0.41 mm
23%
0.016" or 0.41 mm
0.018" or 0.46 mm
21%
0.018" or 0.46 mm
0.020" or 0.51 mm
19%
While a seemingly minor adjustment, increasing a nozzle orifice size by only 0.05 mm (or 0.002 inches) could raise the adhesive amount significantly and generate more waste, if not needed. While this can also be seen in a rise of adhesive costs, there are also some additional quality issues arising from an increased nozzle orifice size.
Changing the orifice size for a hot melt adhesive nozzle can impact other areas of the packaging line. Set speed is often impacted when nozzle size is increased or decreased. 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 because it influences the package seal. Some guidelines to remember:
- Increasing the nozzle orifice size will apply more adhesive and slow down the set speed. The increased adhesive amount lengthens the time it takes for the adhesive to become stronger than the surface it is bonding and produce fiber tear. Pop opens could occur if the adhesive does not set fast enough.
- Decreasing the nozzle orifice size will apply less adhesive and shorten the set speed. The reduced amount of adhesive could cool off too quickly before bonding and cause pre-set issues.
- Adjusting the compression time or belt speed on the packaging line may be needed to counteract a change in nozzle orifice size. If proper adjustments are not made, pop-opens will likely occur.
Nozzle size, tank pressure and adhesive operating temperature work together to influence application. When making changes to a nozzle orifice size, it is important to consider adjustments to tank pressure or application temperature. If the application needs a larger nozzle orifice while maintaining consistent application amount, it is recommended to decrease the tank pressure in 5 psi (0.34 Bar) intervals. At the same time, the application temperature can be slightly decreased by 3oC – 5oC (5oF – 10oF). The temperature adjustment should be done in small degrees while staying within the recommended operating temperature. It is not recommended to run the adhesive at temperatures outside the set ranges as outlined in the technical data sheet.
Hot melt adhesives, like TECHNOMELT®, are dispensed by extruding a continuous stream of material. Increased nozzle orifice size will release more adhesive to the substrate. This excess adhesive can cause stringing, which is a common application process challenge. In many cases the adhesive will create webs of fine adhesive strings in the production area. This additional adhesive can also squeeze out between the package’s flaps once it is sealed. This squeeze out could coat the conveyor belts or the machine, as well as affect the overall package appeal and aesthetics.
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 nozzle size is between 30mm to 45mm (0.012 inches – 0.018 inches), as mentioned previously. If a hot melt nozzle continuously clogs, there may be another issue at play such as char in the hoses or nozzles. If excessive pressure is needed to overcome this blockage, it is recommended to thoroughly investigate the 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. To gain more insights on ways to increase efficiency of hot melt adhesive, register for Henkel’s digital training platform and learn more best practices about improving the operating life of adhesive.
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