This paper relates to a process for preparation of a coating soluble in aqueous alkaline solution, which didn't dissolve in almost all organic solvents and neutral water. The coating composition comprises a poly(acrylic acid-diacetone acrylamide) and isonicotinyl hydrazide as the cross-linking agent. The two components were dissolved in 3-methoxypropanol to prepare the coating solution, which was applied to a grained and anodized aluminum substrate and then dried at 110 °C to obtain the final coating. There exists intermolecular hydrogen bond between the pyridine ring of the cross-linking agent and the carboxylic acid of the polymer. Furthermore, the in-situ chemical reaction between the hydrazide group and the carbonyl group provided the hydrazone bond during drying. The co-action of the physical and chemical cross-linking rendered the coating insoluble in general organic solvents. However, when the coating was exposed to aqueous alkaline solution, the hydrogen bond was broken immediately due to the ionization of the carboxylic acid group, leading to quick dissolving of the coating. The coating might be used in the pretreatment of the aluminum substrate of CTP plates or as the under-layer for the production of double-layer imaging system, and was found very effective in promoting the aqueous alkaline solubility of non imaging area upon development after laser imaging.
Jialing Pu, Zhongxiao Li, "An In-situ Formed Cross-linked Coating and Its Effectiveness as Under-layer in Laser Imaging" in Proc. IS&T Int'l Conf. on Digital Printing Technologies and Digital Fabrication (NIP28), 2012, pp 284 - 286, https://doi.org/10.2352/ISSN.2169-4451.2012.28.1.art00003_2