Features of the Application of Polyurethane Ionomers as Binders in Pigment Compositions for Printing
Authors: Mishchenko Anna, Mishchenko Elena, Tkach Valentina, Kachuk Daria
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The features of formation of polymer films from aqueous dispersions of polyurethane ionomers and the possibility of resolving a number of technological problems of pigment printing due to specific properties acquired by polyurethanes when ionic groups are introduced into their macromolecules are showed in the paper. A feature of the investigated aqueous dispersions is their lyophilicity, which is due to the introduction of ionic groups in salt form into the polymeric chains. Due to lyophilicity, film formation from these dispersions proceeds through the stages of formation of intermediate reversible gels with flocculation contacts, which easily break down. It is shown in the article that this property of dispersions of polyurethane ionomers provides to printing compositions on its’ basis the ability to be easily removed from working areas of printing equipment when it is washed, significantly extends the service life of printing templates, eliminates the build-up of binder polymer, and the need to add special substances to print compositions for this goal, which reduce the stability of colors.
It is shown that the character of the ionic group of a polymer affects the rate of formation of films: it is higher for dispersions of carboxyl-containing polyurethane than for dispersions of a sulfo-containing polymer, which is especially evident in the second stage of the formation of a film on which the gel is compressed. At this stage, the rate of water removal from the gel of the anion-active sulfonated polymer is half as much as that of the gel formed from the polyurethane containing the carboxyl group in the salt form.
The formation of films of anionic dispersions of polyurethanes through the stage of intermediate gel formation extends the shelf life of paints without changes of the printing and technical properties.