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Summary:
To predict press performance of an ink, we must be able to measure accurately its viscosities over such a wide shear rate range. Rotational rheometers equipped with a cone-and-plate or a narrow-gap concentric cylinder geometry are very useful for accurately determining the viscosity of newsinks over a relatively wide range of shear rates. Because of their limited shear force capacity, these instruments are applicable only to low shear viscosity measurements for most commercial inks. When high shear measurements are possible, they fail to produce meaningful data because highly viscoelastic commercial inks tend to crawl out of the measuring gap as the shear rate exceeds a critical value. This phenomenon is known as shear fracture or Weissenberg effect. Axial viscometers, such as falling rod viscometers, have been widely used in the ink industry. They are capable of making accurate viscosity measurements at relatively high shear rates due to the absence of shear fracture. A computer-controlled, axial viscometer was recently developed to overcome these difficulties. Its features are fully explored in this paper. Axial viscometers, such as falling rod viscometers, have been widely used in the ink industry. They are capable of making accurate viscosity measurements at relatively high shear rates due to the absence of shear fracture. A computer-controlled, axial viscometer was recently developed to overcome these difficulties. Its features are fully explored in this paper. A wide variety of inks ranging from newsinks to driographic inks were studied. Together, they form a complete profile curve of viscosity versus shear rate. Viscosity profile curves of those inks are presented in this paper. Correlation of measured rheological parameters with ink performance on press are also discussed.