The Effects of Web Tension on Tack Forces During Printing


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Harrison R. Gates and Douglas W. Bousfield


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The force required to separate a web stuck to a roll is generated by the negative pressure the adherent fluid applies to the web.  The maximum negative pressure, called tack pressure, is an important indicator of maximum stress applied to the web surface during converting operations such as printing, coating, and adhesive processes.  Tack pressure is measured with flush mounted pressure transducers when a web is present in the nip.  It is influenced by a number of process parameters including viscosity, velocity, web tension, takeoff angle of the web, and roll cover compliance.  The shape of the pressure distribution through the nip changes when a web is present.  A simple expression was found to correlate the tack pressure with other parameters for both Newtonian and shear thinning fluids without a web (Gates and Bousfield, 2015).  In this paper, this expression was extended to account for studies where a web influences tack pressure through web material properties and takeoff angle of the web take-up roller relative to the nip.  Takeoff angle can affect shear forces applied to the fluid by the web, which in turn can influence tack development and actual web release angle from the inked roll surface.

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