Lithographic Emulsion Rheology at Low and High Shear Rates

Details:

Year: 2000
Pages: 16

Summary:

The rheology of emulsions of water in varnish and water in complete lithographic ink was measured at shear rates covering the range 10-2 s-1 - 104 s-1 and compared with the behaviour of unemulsified samples. The low shear measurements were made with a conventional rotational rheometer. High shear measurements were made using a 'Multipass' capillary apparatus. The presence of water droplets always increases emulsion viscosity at low shear, and the effect is in many cases well predicted by the Batchelor equation. At high shear rates measured emulsion viscosities are usually lower than for the unemulsified ink. The reasons for this behaviour are discussed, and where appropriate evidence for microstructural change is presented. Inks for which there is a large change in viscosity upon emulsification tend to be more difficult to print and are susceptible to loss in density as the water feed is increased.