Thursday 14 April
Session 3 – Materials & formulation
Session Chair - Holly Steedman
UV radiation cure raw material solutions for inkjet
Tracey Norton
Technical Product and Services EMEA, IGM Resins
Tracey Norton covered UV radiation cure materials and the potential in inkjet inks for increased production speeds, printing onto a wide variety of substrates and reduced VOCs. Monomer and photoinitiator choice for UV inkjet is critical, defining the physical and curing properties of the ink. Newer materials are being introduced which overcome some disadvantages of traditional materials and provide a wider choice of functionalities for ink formulation. For photoinitiator selection, a number of factors need to be taken into account including matching with the curing lamp, required cure speed, toxicity and odour, stability etc. LED curing is becoming increasingly prevalent with its advantages of low energy usage and compatibility with heat sensitive substrates. There are some challenges, as LED cure inks tend to be more susceptible to oxygen inhibition and require photoinitiators specifically matched to their spectral output. Methods to overcome oxygen inhibition were discussed, on the formulation side as well as system solutions such as using an inert atmosphere. Food packaging and migration issues were also discussed, and some low migration photo initiator materials proposed.
Polymer degradation and the role of chain architecture in inkjet printing
Prof Stephen G. Yeates et al., University of Manchester (in collaboration with ITECH Textile and Chemical Institute and Domino UK)
Steve Yeates reviewed the use of long chain polymers in inkjet inks. Addition of a small proportion of polymers to inks is found to help drop formation after jetting, but it is found that degradation of the molecular chains occurs due to flow through high shear constricted geometries that are an integral part of an inkjet system. This degradation limits the beneficial effect the polymers have. The mechanism of degradation is believed to be mainly constrictional shear flow in DOD systems, while in CIJ systems long term mechanical degradation in filters is the main mechanism. Steve showed how using hyperbranched polymers exhibited different behavior, with a higher concentration of polymer needed to show the same viscoelastic effect, but with significantly less degradation observed.
Super wetting surfactants for water-based ink applications
Roger Reinartz
Lead Research Chemist, Additives Europe, Air Products and Chemicals
Roger Reinartz reviewed the use of surfactants in aqueous inks, and their role in controlling wetting of the ink on the substrate, with good wetting occurring when the ink has a lower surface tension than that of the substrate and retraction occurring when the ink has higher surface tension. The action of surfactants on surface tension is dynamic, with different surfactants moving at different speeds leading to distinct rate dependent viscosities. Superwetting surfactants have compact hydrophobes that pack efficiently at interfaces and move quickly, giving very low dynamic surface tensions and fast wetting times. Roger reviewed some examples of these materials and highlighted the advantages for inkjet inks, especially when printing onto lower energy substrates which is often presents a challenge.
Inkjet printing beyond colour: efforts to go lab-to-fab
Prof Dr rer nat Reinhard Baumann
Department of Digital Printing and Imaging Technology, Technische Universität Chemnitz
Prof Baumann reviewed the key challenges of functional printing. He pointed out that in colour printing, image quality is achieved by masking defects from the human eye. Conversely, in functional printing generally these defects cause a genuine problem and need to be eliminated rather than masked. Reinhard proposed a future vision of printed smart objects as part of the ‘internet of things’, which calls for a wide variety of printed functionality and therefore of inks and systems to print these. One of the key challenges is printing metallic inks and recovering conductive behavior, with various solutions proposed and reviewed by Reinhard. An additional challenge is in creating printed circuits, where different materials need to be deposited onto the same substrate. Reinhard showed an example of inkjet printed thin-film transistors printed in 6 TFT arrays with a yield of 80-90%. A gas sensor using printed carbon nanotubes was also shown.
Dispersion and stability in formulated systems
Graham Worrall
Principal Scientist, Centre for Process Innovation
Graham proposed a methodology for formulation across multiple applications with some key steps: know your target, formulate, apply and process, and then test. Stability is particularly important in dispersed systems, and Graham outlined the DVLO theory that governs the stability of particles in dispersion, distinguishing reversible flocculation from irreversible coagulation. The introduction of a repulsive force from an electrostatic or steric effect is used to provide stability. Graham discussed the use of Zeta potential to measure the stability of dispersions and its effect in metal oxides, where similar potentials lead to stability but opposite charges give hetero-aggregation. Graham also discussed the rheology of dispersions, with dispersed systems typically showing shear-thinning behavior.
Formulating inkjet inks for material deposition applications - challenges and opportunities
Dr Alan Hudd
Founder & Director, Alchemie Technology
Alan discussed recent trends in printhead developing, with smaller drop printheads being developed for graphics applications – meanwhile larger drop printheads are also required for industrial decoration and functional applications. Alan also surveyed the rapidly broadening range of applications for functional inkjet printing, mentioning printable pills for drug dispensing and printing of graphene amongst others. The rapid growth of the ceramic printing market was also reviewed, with the technology challenges discussed as well as how these were overcome. Alan discussed the properties of graphene which are exciting for many applications, and also the challenges of formulating inkjet inks based on this material while maintaining its properties.
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Tim Phillips & Kirsty Inman, IMI Europe and Holly Steedman, Indujet