Certain colorants become insoluble under specific and well-defined pH conditions. By forcing a colorant to become insoluble on the page, migration of the colorant is inhibited, thereby helping to reduce bleed between inks of different colors. The colorant is forced out of solution from the ink by contact...http://www.google.de/patents/US5320668?utm_source=gb-gplus-sharePatent US5320668 - Bleed alleviation using pH-sensitive agents
