Online Spectroscopic Monitoring in Recycled Stock Preparation Systems
Online spectroscopic sensors in recycled stock preparation provide continuous measurement of micro-stickies and fillers to optimize chemical dosing and yield.
Polyvinyl Acetate
Adhesive Bond
Thermoplastic resins synthesized from the polymerization of vinyl acetate monomers create a strong bond between paper and board surfaces. Converting plants use polyvinyl acetate as a cold set adhesive because it provides excellent adhesion to porous substrates and dries quickly through the loss of water. The resulting film is clear, flexible and resistant to many oils and fats.
Shear Resistance
Molecular interaction between the resin and the cellulose fibers creates a permanent mechanical and chemical link. Since polyvinyl acetate penetrates the surface of the paper, the strength of the joint often exceeds the internal tear resistance of the board itself. Formulations are adjusted with different solid contents to match the speed of the folder gluer and the absorbency of the linerboard.
Setting Speed
Rapid evaporation of the water carrier allows the adhesive to reach its handling strength in a few seconds. Because polyvinyl acetate is a water based emulsion, the ambient temperature and humidity of the factory floor influence the time required for the bond to cure. High speed packaging lines require precise control over the application volume to prevent the glue from squeezing out or failing to set before the carton reaches the packing station.
Flaps on a corrugated carton spring open during the final stages of the folding process when the adhesive fails to reach its handling strength.