engleski

DYNAMIC CONTACT ANGLE AS A METHOD IN GRAPHIC MATERIALS CHARACTERIZATION

Surface properties of the materials play very important role in their usability in many industries. The best example in graphic arts industry is lithographic printing where printing process is based on the opposite surface properties of the printing and nonprinting areas on the printing plate. Another aspect of the surface phenomena could be seen in the ink acceptance on the printing substrates in conventional and digital printing techniques. This makes determination of the surface properties and wetting characteristics of the solid materials and properties of the liquids very significant. Contact angle is the value which determines wetting characteristics between observed solid and liquid as liquid drop forms different shapes depending on the solid surface. It is known that formation of the liquid drop’s shape is a dynamic process. One differentiates two contact angle values, static one, measured when the drops shape is stable and dynamic one, where measurement of the contact angle is varying in time from applying the liquid on the solid surface. But beside time variation, one could measure advancing and receding contact angle when liquid is added and sucked back from the surface, respectively. The aim of this paper is to perform evaluation of the applicability of dynamic contact angle determination in characterization of the surface properties of graphic materials. For that purpose a set of the offset printing plate was prepared by immersing them into developing solution made of sodium metasilicate. Measurements of the time dependant and advancing and receding contact angle were performed by applying redistilled water on the image areas of the prepared printing plate samples. Results of the investigation showed that the time dependant contact angle is similar on all printing plate samples and is not depending on the value of the contact angle. The value of the contact angle hysteresis is smallest on the unprocessed printing plate, but it decreases by increasing the developing time. Obtained results showed that observing time dependant contact angle one could not detect all changes of the printing plate’s surface due to the chemical processing. The value of the contact angle hysteresis is implying the change of the surface roughness and therefore could be useful tool for the surface analysis of the printing plate. But to confirm that results, one should take further research including performing other methods for surface characterization to confirm usability of the dynamic contact angle in graphic materials characterization.

wetting; dynamic contact angle; printing plate; material characterization

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