Printing inks and printing methods employing the same

Claim 1

In a process for printing surfaces by an intaglio or flexographic printing process, the improvement wherein a solvent-free printing ink, solid at room temperature but molten at printing temperatures, is employed, said ink having a viscosity of not more than 0.5 Pas at printing temperatures and comprising a pigment and a thermoplastic binder having a softening point between 90° C. and 160° C., said binder comprising a synthetic resin having an average molecular weight between about 1500 and 3000 and being selected from the group consisting of polyamide resins and polyesteramide resins, said polyamide resins being the condensation product of approximately equivalent amounts of (1) an acid component comprising a dimerized fatty acid and a monocarboxylic acid and (2) an amine component comprising a diamine, and said polyesteramide resins being the condensation product of approximately equivalent amounts of (1) an acid component comprising a dimerized fatty acid and a monocarboxylic acid and (2) an amine component comprising a diamine and at least one member selected from the group consisting of diols and alkanolamines, said acid component (1) of said polyamide and polyesteramide resins optionally comprising co-dicarboxylic acids and cyclic acid anhydrides, the equivalence ratio of the combined dimerized fatty acid and optional co-dicarboxylic acid to the total monocarboxylic acid and optional cyclic acid anhydride being from 0.5:0.5 to 0.3:0.7.