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Content archived on 2024-06-18

Development of sol-gel inkjet inks for printing on glass substrates for architectural applications

Final Report Summary - TIGJET (Development of sol-gel inkjet inks for printing on glass substrates for architectural applications)

Sol-gel technology has attracted significant attention of researchers as a low temperature chemical method of synthesis that assures modifications on molecular level and does not require expensive and power-consuming equipment. Wide range of sol-gel derived systems has already found its practical application as self-cleaning and antifogging coatings, antireflective coatings, corrosion protective films, photocatalytically active films and powders, catalysts, sensors, decorative coatings, etc.

The possibilities of manufacturing individually designed flat glass in the architectural area are very limited at the moment. Especially, outdoor applications present great challenge due to the severe weathering conditions including UV-light degradation and poor humidity adhesion of inks to glass. One of the possible approaches to improve the weathering properties of the decorated glass is to assure covalent bonding between coating and glass surface. Due to their known high affinity to glass and ceramic surfaces, sol-gel derived compositions are systems of choice when strong covalent bonding between glass and decorating medium is required.

The project TIGJET (reference No. 235923/909923) supported by a Marie Curie International Incoming Fellowship within the Seventh Framework Programme of the European Commision. The research efforts have been directed onto introduction of sol-gel derived materials into industrial application through the development of a new class of sol-gel inkjet inks which opens a new way of manufacturing individually designed flat glass for outdoor applications. Developed hybrid organic-inorganic sol-gel inkjet inks are applicable with a wide range of drop-on-demand print heads and show on the one hand excellent adhesion to glass and metal surfaces and on the other hand withstand exterior weathering conditions which are typical for permanent usage on facades over years.

Sol-gel inkjet inks were formulated on the basis of UV-curable organoalkoxysilanes and multifunctional acrylates, urethane acrylates. The mixture of free radical photoinitiators for surface and through cure and photoacid generator were used for drop fixation during UV-irradiation of the inks.

Photo-induced sol-gel process has been utilised in the development of the sol-gel ink-jet inks for printing on glass as it assures that the sol-gel transition of organosilanes happens just after the ink arrives the substrate and absorbs UV-light. In this way, it was possible to overcome the issues related to the stability of classical sol-gel systems when sol-gel transition is initiated by acid / base catalysts added to the composition and as a result of hydrolysis / condensation processes taking place the viscosity of the systems changes drastically. The latter is dangerous for print heads controllable performance due to their blockage during operation or in the stand by mode.

Significant humidity resistance of the hybrid sol-gel inkjet inks printed on glass surface that reaches more than 1000 hrs (40oC, 100 % RH) and acceptable UV-light fastness, especially when modified with inorganic pigments, make them product of choice for glass decoration for indoor and outdoor usage achieving economic and flexible custom made designs.

The way of production of hybrid sol-gel inkjet printable layers with metal nanoparticles (NP) has been developed where in-situ generation of gold metal NP takes place simultaneously with UV-light induced hydrolysis of organofunctional silanes and UV-curing of acrylics. The formation of uniformly distributed gold NP within sol-gel films depends on the time of UV-irradiation. At the same time, as the thermal curing step of the hybrid sol-gel inkjet inks is presupposed, it was figured out that the UV-curing stage could be reduced up to the time necessary for ink drop fixation on the substrate (at this moment initial photoreduction of Au(III) ions occur) further reduction of aurum ions happens during thermal treatment of the sol-gel films. Thermally cured sol-gel inks containing gold NP have intensive magenta colouration due to the surface plasmon resonance absorption characteristic for Au NP.

The photo-induced sol-gel trasition of organosilicas looks to be the process of choice where the classical sol-gel process could not be applicable due to the composition stability restrictions like in the inkjet printing.

Sol-gel inkjet inks developed in the project are promissing compositions to be applicable with wide format inkjet printers to decorate float glass for architectural applications. The possibility to decorate other nonabsorbing substrates (metal sheets, ceramics, etc.) could be realised as well using developed sol-gel inkjet ink compositions that would broaden significantly application areas.