Adhesive Rheology and Dispensing Process Analysis

The rheological properties and dispensing characteristics of three reactive hot-melt adhesives were investigated in this study. Flow experiments were carried out in the temperature range from 60 °C to 110 °C. The Casson equation was used to represent the flow curves of the materials exhibiting an apparent yield stress and a plastic viscosity. The temperature dependence of the apparent yield stresses and the plastic viscosities of the reactive hot-melt adhesives were evaluated. Similar to epoxy paste adhesives, the yield stresses of the reactive hot melts are much less sensitive to temperature than the plastic viscosities. The sensitivity of the chemical cross-linking reaction was investigated using Differential Scanning Calorimetry. Processability of the reactive hot melt adhesives has been compared with that of the conventional paste materials using a quantitative model describing the paste material dispensing system. The reactive hot melt adhesives are much more susceptible to viscous dissipation than paste adhesives and their process windows are consequently much narrower. Modifications of the dispensing system to reduce the residence time at elevated temperatures should improve the processability of the reactive hot-melt adhesives.