In our new series of articles, we focus on characteristics of adhesives and their impact on gluing performance. Tap into a wealth of our expert-driven insights about the gluing process, starting with the glue viscosity.
Viscosity plays a pivotal role in the performance of hot melt adhesives (HMAs) and their compatibility with FELIX GLUER plotters. It influences the adhesive’s application, flow behavior and ultimate bonding quality. Selecting an HMA with the appropriate viscosity ensures seamless operation and optimal performance of your glue plotter. But what exactly is viscosity?
Viscosity breakdown
We have sat down with our Adhesive Business Unit Director Berk Baltaci, to further discuss the key factors of the gluing process.
Starting from the basics, what is viscosity?
Berk Baltaci: Viscosity is a fluid's resistance to flow. In simpler terms, it measures how "thick" or "thin" a fluid is. A high viscosity fluid - like honey - flows slowly, while a low viscosity fluid - like water - flows quickly. For HMAs, viscosity determines how well the adhesive can be applied through the applicator of the plotter and how it interacts with the substrate to form a strong bond.
If adequate level of viscosity is needed to optimize the gluing process, then which factors affect the HMA viscosity the most?
Berk Baltaci: Factors that are crucial to selecting the right HMA for your application would be - first and foremost - temperature, shear rate, and the adhesive’s composition. Regarding the temperature, HMAs need to be maintained within an optimal temperature range during application to ensure consistent flow and bonding. Overheating can degrade the adhesive, while insufficient heating increases viscosity, hindering application.
The type and concentration of polymers, resins, and additives in the adhesive formula directly impacts its viscosity. For instance, adhesives with higher polymer content tend to have higher viscosities, offering stronger bonds but requiring higher application temperatures. Finally, as HMAs are pumped or extruded, the shear forces reduce viscosity temporarily, a phenomenon known as shear thinning. This ensures smooth application at higher speeds.
