2023 Volume 96 Issue 1 Pages 2-8
Cellulose materials are being reviewed as a printing material for packaging containers. The trade-off between image density and rub resistance is an issue for cellulose materials, as typified by paper. In this study, among intermolecular forces, we focused on the CH/π hydrogen bonding force, which is not easily affected by water, and focused on the direct dye structure that enables the CH/π hydrogen bonding force to work on the cellulose backbone. The rub resistance was improved by imparting the direct dye to the printing paper in advance, and was further improved by incorporating the direct dye structure into the polymer dispersant. As a direct dye structure superior in rub resistance, we found the following four points, referring to the electrophilic aromatic substitution: (1) having a long conjugated double bond backbone, (2) having many electron-donating substituents, (3) having a low sum of intramolecular substituent constants, and (4) having an asymmetric structure.
Colorants with Direct Black 22 introduced into polymeric dispersants that meet these four conditions exhibit both high print density and excellent rub resistance.
