Low‐speed tack measurements of fluids and inks

Abstract

SYNOPSISLow-speed tack measurements (x 0.1-6.0 rad/s or = 1-57 RPM) have been determined for polymeric-based solution inks and oil-based dispersion inks, tripropylene glycol (TPG), , and N-350 (viscosity calibration standard) fluids using a metal roller/incline method. The inks and fluids were tested under "unaged" or reference conditions at 25°C. The inks were "aged" at 70°C and, subsequently, tack measurements were made at 25°C. The tack (7,) and angular speed (wi) for the inks were empirically fitted as functions of incline angle (a) and "aged" time, tea. A correlation was also made for tack and percent weight change, A W,. Other factors, such as viscosity, surface tension, humidity, and "aging" temperature, Ted, were also found to affect the magnitude and variation of tack. Additionally, the results suggest that low-speed tack measurements are quite useful for selecting solution inks containing polymeric substances that possess the desirable spreading, mixing, and pressing properties in high-speed/high-volume printing and the component compatibility I NTRO DUCT1 0 NThe resistance of the motion of a solid surface in contact with a fluid can be defined as tack or "stickiness" of the fluid-solid interface.14 This property can be measured from parallel-plate separation at a given rate or from rotational torque experiments (balls, rings, cylinders, etc.) .',' The forces in the rotational torque experiment can be generated by an external source (e.g., torque motors) or by gravity. In flexographic printing applications, it is often important to know the "splitting" characteristics of a fluid or ink on rotating rollers or the transfer of ink to printing surfaces at high rates ofThe theoretical analysis of splitting in a rigid nip by a rheological material may be described by the Navier-Stokes hydrodynamical equation.' Low-speed tack measurements can be used for composition differentiation of inks with desirable properties of viscosity and surface tension' and the mixing, spreading, and pressing characteristics of solutions containing polymeric substances and other type substances such as In ink formulation, for example, fluid substances may be selected to meet the overall desired tack lev-* To whom correspondence should be addressed.Journal of Applied Polymer Science, Vol. 58,881-895 (1995) 0 1995 dohn Wiley & Sons, Inc.CCC 002 1 -S995/95/050881-15 els for specific purposes such as torque reduction for "data" wheel printing, the control of dust levels from paper substrates resulting from high speed and high volume printing, and long-term tack stability. For a sizable number of formulations, one would prefer that this screening process be simple and reliable. In order to address this problem, we designed a roller/incline device that could determine fluid tack over a range of relatively low rotational speeds by changing the incline angle, a. In this paper we present some of our preliminary findings6 and show how tack influences the rotation of a moving solid surface in contact with a stationary fluid surface and ho...