A Driving Method for Reducing Oil Film Splitting in Electrowetting Displays

Electrowetting displays (EWDs) are one of the most potential electronic papers. However, they have the problem of oil film splitting, which could lead to a low aperture ratio of EWDs. In this paper, a driving waveform was proposed to reduce oil film splitting. The driving waveform was composed of a rising stage and a driving stage. First, the rupture voltage of oil film was analyzed by testing the voltage characteristic curve of EWDs. Then, a quadratic function waveform with an initial voltage was applied at the rising stage to suppress oil film splitting. Finally, a square wave was applied at the driving stage to maintain the aperture ratio of EWDs. The experimental results show that the luminance was increased by 8.78% and the aperture ratio was increased by 4.47% compared with an exponential function driving waveform.

Analysis of the shortness of offset ink as a function of tack on paper by comparing elastic and Hencky strain extension

We conducted a study to differentiate between the effects of the extensional length of an offset ink and its film split tack behavior related to the blanket paper ink film separation on a press. Two separation techniques were used to study these phenomena separately: constant force and thus varying acceleration, giving sensitivity biased toward ink length; and constant extensional strain rate (Hencky strain rate), giving sensitivity biased toward ink on paper tack and viscosity. In general, high intrinsic ink tack level seems to correspond to high ink on paper tack value. Both methods identify the tack cycle as ink oil is removed by capillary action into the substrate. The extensional strain rate matches more closely the film splitting effect of the print cylinders, identifying effects of extensional viscosity. In contrast, the constant force technique is sensitive to length of an ink as a result of tack build. A range of inks of different shortness (inverse length) was analyzed using the two methods on coated paper. Development of tack differed for the range of inks according to shortness, and thus the way they responded to the two measurement techniques. Differentiation was obtained between the behavior during tack rise, the balance between adhesion and maximum internal tack, and the tack fall over time. The development of shortness as a function of ink on paper tack provides new insights into the basis for piling, paper strength demands, and runnability under different press dynamics.

Capillary and Viscoelastic Effects on Elastohydrodynamic Lubrication in Roller Nips

A viscocapillary model of liquid movement and film-splitting in deformable nips between an elatomer-covered roll and a hard roll is presented here. This “soft” elastohydrodynamic regime is described by Reynolds’ equation of lubrication flow and a simple set of spring-and-dashpot elements for the viscoelastic behavior of elastomeric roll covers. Capillary effects around the film-split are accounted for with an augmented Young-Laplace equation from film-flow theory. Effects of the liquid’s surface tension (via capillary number) and the elastomeric cover’s relaxation time (via Deborah number) are predicted and compared with available experiments. Application to the flows through the multiple roller nips of printing press systems is discussed.