Understanding how to maintain operating consistency is important. Each equipment manufacturer has best practices to keep the machinery working efficiently. Hot melt spray adhesive issues can result from an over-reliance on generalized guidelines.  These are useful in establishing a starting point; however, it is important to gain a strong understanding of how the multiple variables may impact the process and lead to solutions.  

Viscosity:

Viscosity measures the thickness of the molten hot melt adhesive at a given temperature setpoint. Each hot melt adhesive is formulated for specific finished good requirements, bond strength, substrate adherence, etc. and application method spray versus slot coating. The hot melt adhesive tank temperature should be set within the recommend operating range to achieve the ideal viscosity for the application technology used. 

Flow Rate:

Flow rate is the amount of adhesive being metered out to the substrate via the spray process and is controlled by the hot melt adhesive tank. When flow rates are too low, results can include poor adhesive distribution, weak bonds or overspray. A mismatch between nozzle orifice size, viscosity and flow rate can cause pattern issues that are difficult to remedy. 

Nozzle Type:

Spray nozzles are designed to emphasize a specific performance characteristic, from clog-resistance to bond strength. A mismatch of technology to application variables (e.g., flow rate) could result in a process issue. When required, changing spray nozzle types typically requires minimal time and capital investment. 

Nozzle Height:

Nozzle-to-substrate distance can be critical to performance. For some technologies, this dimension has a direct impact to pattern width – positioning closer to the substrate reduces spray width. For others, an incorrect setting can result  in overspray as the pattern “floats” above the substrate.

Pattern Air:

Used to manipulate the hot melt adhesive as it exits the spray nozzle, pattern air spins or oscillates a bead of adhesive  and produces a pattern on the substrate. The setting is critical. It must be balanced with the viscosity and volume of hot melt  adhesive for each application, along with requirements such as width or coverage density. With adhesive flow rate and nozzle type being fixed values, the correct amount of pattern air is tied to the application temperature of the hot melt adhesive. 

Hot melt spray adhesives, like TECHNOMELT, have a range of operating conditions. The key to a robust process is matching the abovementioned process variables to the adhesive, resulting in application consistency, proper equipment functionality and an efficient production line.