Apparent viscosity at the relatively high shear rate of 2500 s⁻¹ does not completely define the rheological properties of printing inks but is useful in the practical control of ink viscosity during production and the specification acceptance between supplier and purchaser.

The slope of the power law plot is the preferred measure of non-Newtonianism. The yield value, which is obtained by extrapolation of high-shear measurements to a shear rate approaching zero, does not conform to the definition of the true yield stress (see 3.1.7). The yield value and other low shear parameters are also subject to a high degree of variability (see the precision table in Section 17).

1.1 This test method covers the procedure for determining the falling-rod viscosity and degree of non-Newtonian behavior of printing inks, vehicles, and similar liquids that are essentially nonvolatile and unreactive under ordinary room conditions.

1.2 For printing inks, which are typically non-Newtonian, this test method is applicable in the apparent viscosity range from about 10 to 300 P at a shear rate of 2500 s¹. For Newtonian liquids, the applicable viscosity range is about 10 to 1000 P (1 P = 0.1 Pas).

1.3 This test method uses a falling-rod viscometer in which shear conditions are altered by manually adding weight to the rod. A fully automatic instrument is described in Test Method D 6606.

1.4 This test method, as does Test Method D 6606, bases calculations on the power law model of viscosity. ISO 12644 covers not only the power law but also the Casson and Bingham models.

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific hazard statements, see Section 8.