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Tuning the mechanical performance of UV-cured polyurethane coatings

Modifying compsotion of the reactive diluents
: Zvonkina, Irina; Hilt, Michael

Hilt, Michael (Chairman) ; Fédération d'Associations de Techniciens des Industries des Peintures, Vernis, Emaux et Encres d'Imprimerie de l'Europe Continentale -F.A.T.I.P.E.C.-; Gesellschaft Deutscher Chemiker -GDCh-, Frankfurt/Main; Gesellschaft Deutscher Chemiker -GDCh-, Fachgruppe Lackchemie; Verband der Ingenieure des Lack- und Farbenfaches; The Oil & Colour Chemists' Association -OCCA-:
New functions and sustainability - drivers for future coatings : European Technical Coatings Congress, 3-5 September 2014, Cologne, Germany
Frankfurt am Main, 2014
23 Folien
European Technical Coatings Congress (ETCC) <2, 2014, Cologne>
Conference Paper
Fraunhofer IPA ()
UV curing; polyurethan; coating

UV cured coatings attract considerable attention in science, technology and in industry, such as automotive, architectural and packaging. Main benefits of UV coatings compared to coatings obtained using other energy sources are their environmentally friendly nature, shorter curing time, presumably lower energy consumption, longer pot life and other [1-2]. Despite some challenges related to UV cured coatings that need further investigation and new solutions, the market of UV cured coatings is growing.
For optimisation of a composition for UV cured coatings, it is of interest to investigate the effect of reactive diluents on the structure and properties of the coatings. To tune the performance of UV cured coatings based on polyurethane oligomers, the structure and properties of the coatings were modified by altering the amount and functionality of acrylic reactive diluents, without changing the nature of oligomers. The proposed approach of modifying the coating structure affecting the mechanical properties, rheological behaviour and adhesion of the coatings has benefits due to a possibility of maintaining the advantages of the selected chemical structure of the oligomer.
The effect of a composition of two-/three-functional low-molecular weight reactive diluents on the curing kinetics, rheological behaviour, mechanical properties and adhesion of UV cured coatings applied on polymer substrates has been systematically investigated. The changes in the properties are related to alterations in the curing process and in the structure of the coatings.
Traditionally, except for only a few approaches described in the literature [3-4], monomers are used in compositions for UV coatings mainly for improvement of the technological characteristics of the coating application, related, mainly, to their rheological behaviour. New findings demonstrate, in addition to an exponential decrease in viscosity and a proportional growth of enthalpy of the exothermic photopolymerization reaction during coating formation, alterations in other coating properties with increasing content of a reactive diluent.
Changing monomer contents leads to alterations in the coating structure, a gradual increase of the glass transition temperature and changes in elasticity and other mechanical properties of the coatings. This corresponds to a gradual improvement of coating adhesion to a polymer substrate. The relation between the rheological behaviour, mechanical properties and adhesion of coatings has been demonstrated. Based on the results of the study, the desired properties of UV coatings can be modelled and controlled without changing the nature of a particularly selected oligomer, thus maintaining its benefits in a coating composition.