Effectiveness of Acrylic Polymers in Water-Based Pigment Dispersions — A Taguchi Approach

Abstract

Pigment dispersion is a critical step in manufacturing printing inks. Styrene/acrylic copolymers and acrylic polymers are the common water based resins used in the graphic arts industry to disperse pigments. While surfactants may aid in pigment dispersions, complete surfactant grind pigment dispersions are only used in special applications. In this paper, three styrene/acrylic copolymers and two acrylic polymers with molecular weight (M_n) ranging from 1,700 to 4,800 and 25,000 to 42,000 respectively were evaluated in pigment grinding. Carbon black was chosen as the pigment because black is one of the colors used in largest volume in printing inks. Original layout of the experiments will require a total of 4374 (6¹ × 3⁶) trials to cover all the combinations that it intends to study. Instead, the Taguchi’s Orthogonal Array experimental design was employed. An L18 (2¹ × 3⁷) design was chosen and modified as L18 (6¹ × 3⁶). This technique enables us to study one factor at six levels and six factors at three levels each by performing eighteen experiments only. It was found that styrene/acrylic copolymers provide high jettness and gloss for the black grind. Acrylic polymers develop higher color strength than the copolymers. The pigment to binder ratio (range from 5/1 to 3/1) and grinding time (10 to 30 minutes) had no effect on the quality of the pigment dispersions. The resins studied are all effective within these constraints. The defoamer and surfactant used in this study showed an adverse effect on the dispersions.