US Patent 7910635 Shear resistant printing ink vehicles

The specification describes a process for making gelled ink resins which exhibit improved properties such as lower viscosity under low shear and less viscosity decrease with increasing shear. In a preferred embodiment, a rosin-based or hydrocarbon-based resin is mixed with an organic solvent and reacted with a polyamine reactant, such as melamine-formaldehyde resin or hexamethylene diamine, under conditions sufficient to produce a substantially covalently cross-link gelled resin. The resulting gelled resin resists viscosity breakdown under high shear conditions and may be used directly for making ink compositions, obviating the need for further gelation and avoiding the use of conventional organo-metallic gelling agents.