1. Field of the Invention
The present invention relates to a coloring material having an elasticity and a process for the preparation thereof.
Coloring materials having an elasticity are used in various fields of coloring materials as, for example, bases of paints and inks, and, in particular, the elasticity and the characteristic that the polymer per se is colored of coloring materials of this type make them valuable for use as bases of inks giving erasable written letters or figures.
2. Description of the Related Art
As the ink composition giving letters or figures written on paper by a ball pen or the like which can be easily erased by a rubber eraser within a certain time, there is known a composition comprising a dye or pigment, a solvent-soluble polymer, water or an organic solvent, and other additives. A polymer having an elasticity, that is, rubber, is effectively used as the solvent-soluble polymer. As the rubber-containing coloring composition, there are known a composition comprising a natural rubber or isoprene rubber, a pigment, a low-boiling-point rubber solvent, and other additives (Japanese Unexamined Patent Publication No. 58-208358); a writing liquid comprising a latex including an uncarboxylated styrene/butadiene rubber and a 2-chlorobutadiene polymer and/or vinyl pyridine/styrene/butadiene rubber, and a dye (Japanese Unexamined Patent Publication No. 59-49276); a composition comprising a carboxylated styrene/butadiene copolymer latex and a triarylmethane dye (Japanese Unexamined Patent Publication No.56-131679); and a reaction product of a dye with an addition reaction product of an ethylene-propylene-diene terpolymer (EPDM) and an .alpha.,.beta.-ethylenically unsaturated carboxylic acid (Japanese Unexamined Patent Publication No. 54-17931).
When a pigment is used as taught in Japanese Unexamined Patent Publication No. 58-208358, it is difficult to stably disperse the pigment, the long-term storability is poor, and ink is readily blurred. If a dye is used as taught in Japanese Unexamined Patent Publication No. 59-49276, to moderate these defects, since the dye is merely dispersed in the elastic polymer as the binder, the dye is likely to permeate into paper and the color remains on the paper surface even though an attempt is made to erase written letters or figures. As means for overcoming this defect, there can be mentioned the processes proposed in Japanese Unexamined Patent Publication No. 56-131679 and Japanese Unexamined Patent Publication No. 54-17931. In the former process, the light resistance is insufficient because the linkage is formed between the carboxyl group and the dye, and in the latter process, the manufacturing steps are complicated because the unreacted dye must be removed.