PURPOSE: To obtain the title ink having excellent dispersibility, image quality and durability consisting essentially of a specific reaction product, carbon black and a binder.

CONSTITUTION: The objective ink consisting essentially of a reaction product prepared by reacting an unsaturated bond-containing compound (e.g. 1,9- decadienoic acid) with an organic compound containing a carboxyl group and an aldehyde group (e.g. glyoxylic acid) in the presence of a protonic acid such as sulfuric acid or a Lewis acid such as BF3 or a polymer prepared by coupling an anion living polymer of 1,3-butadiene, etc., with a tin compound such as methyltrichlorotin or an isoprene-based polymer treated with tin tetrachloride, carbon black (amount of carbon black used is preferably 5-40wt.% in ink) and a binder such as carnauba wax.