AVS 56th International Symposium & Exhibition
    Inkjet Technology: Printing, Materials Processing, and Microfluidics Fundamentals Topical Conference Wednesday Sessions
       Session IJ+MN+TF-WeA

Paper IJ+MN+TF-WeA12
Novel Dynamic Volume Control in Jetting of Complex Fluids

Wednesday, November 11, 2009, 5:40 pm, Room B3

Session: Inkjet Printing Technology: Advances and Challenges
Presenter: G.E. Mårtensson, Mydata Automation AB, Sweden
Authors: G.E. Mårtensson, Mydata Automation AB, Sweden
W. Holm, Mydata Automation AB, Sweden
Correspondent: Click to Email
In conventional ink jetting applications, a pressure difference is used to ensure the continuous and prompt filling of the jetting chamber between jetting actuations. The delivery of precise fluid volumes utilizing inkjet-like drop-on-demand jetting technology is primarily controlled by the piezo voltage that actuates the jetting chamber (Gerhauser et al. 1983, SID 83 Digest). The jetting of large volumes, in excess of 1 nL, of complex viscous fluids is complicated by the difficulty of filling the ejection chamber quickly after the previous droplet ejection.

In order to ensure the delivery of fluid to the ejection chamber, a mechanism utilizing a helical viscous pump has been introduced and implemented by the authors. The fluid is fed to the helical pump from a reservoir of fluid stabilized by a regulated reservoir pressure. The flow rate is regulated by the speed of the driving surface of the viscous pump. The ejection mechanism consists of a piezo actuated piston that drives the fluid in the chamber through the nozzle on to the intended surface.

The ejected volume of fluid has been studied with respect to piezo voltage, Vp , pulse time, tp , of the piezo signal and the angular speed of the helical viscous pump. The ejected volume has been estimated from digital photographs taken of the droplet, as well as via 3D profilometry methods. It has been shown in the experimental jetting setup that the volume of a jetted deposit is only affected to a minor degree, of the order of 5% of the goal volume, by the chosen piezo voltage, Vp , acting on the piston. This is also true for the chosen pulse time, tp . The form of the ejected fluid droplet is affected by the pulse time, tp, only for relatively small volumes. Through imaging experiments, it has been shown that the speed of the ejected droplet has a nearly linear response to the piezo voltage, Vp .

The effect of the fluid’s viscosity, represented by its dynamic shear modulus, G*, and its dependancy on rate of shear, dγ / dt , on the ejected volume was also studied. The effect on the delivered volume was slight for the range of non-Newtonian fluids available, in spite of a strong shear-thinning behaviour.