GCM 110 Chapter Notes - Chapter 9: Letterpress Printing, Thixotropy, Rheology
25 Apr 2016
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Pigments: finely divided solid materials + dyes = colour. Pigment characteristics: gravity, particle size, opacity, chemical resistance, dispersibility, and permanence. Colour matching: done by visual comparison under standard lighting conditions using spectrophotometers. Viscosity: measure of the flow characteristics of soft or fluid inks. Letterpress and offset inks are stiff inks that are thixotropic: thick in the can, but under certain conditions will become fluid and flowy. Body: the consistency, stiffness or softness of inks. Length: ability for an ink to flow and form filaments (fibers) Long inks: flow well, form long filaments, but tendency to mist/fly. Short inks: butter-like, poor flow, tendency to pile on rollers and plates. Tack: the stickiness of the ink, or the force required to split ink film between two surfaces. Drying: printing inks dry in ways like absorption, selective absorption, oxidation, polymerization, evaporation, precipitation, and curing by radiation. Letterpress inks: inks designed for printing from raised surfaces.
