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Dave Horwat
Lead Application Chemist |
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How can I improve the spraying of water-based adhesives? |
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The spray process is a very high shear process. Shear rates in a spray head can easily reach 50,000 to 200,000 reciprocal seconds. Significant factors affecting sprayability are the emulsion's solids and the emulsion's viscosity under this high shear. Water sensitivity is also necessary since it influences the self-cleaning aspect of the adhesive and minimizes drying and fouling on the spray tip.
Airflex® 401 emulsion is a 55% solids, low Tg vinyl acetate-ethylene emulsion (VAE) with a low viscosity under shear for good sprayability. It is also water sensitive in the initial stages of film formation to self-clean and hold a consistent pattern. Additional water sensitivity for self-cleaning can be built in by the addition of humectants, like glycerin.
Most high solids/low viscosity VAE emulsions, like Airflex 7200 are inherently more sprayable than thicker emulsions at 55% solids. This is due to their low viscosity under shear which provides a finer, broader spray pattern with smaller spray droplets. Smaller droplets are ultimately faster setting than poorer spraying, higher viscosity adhesives. Sprayability almost always improves with dilution of the adhesive formulation. |
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