Inkjet Ink Development Conference Review - Session 1 - Colorants & Dispersions

On 13-14 April 2016 around a hundred like-minded people convened in Lausanne, Switzerland for IMI Europe’s Inkjet Ink Development Conference. This was a two-day technical conference aimed at inkjet fluid developers across a variety of applications such as packaging, textiles, graphics, functional and industrial printing. Twenty invited speakers gave technical presentations on creating stable dispersions, the impact of additives on formulation performance, raw material quality and consistency for manufacturing, drying and curing of inks and other topical themes. The conference delegates came from a range of companies and universities including ink, dispersions and colorants, equipment and other inkjet printing companies and included many of the big industry names.

Printhead Technology Course presented by Mike Willis

Printhead Technology Course presented by Mike Willis

On the day before the conference we held a free short course on “Printhead Technology for Ink Chemists” which was presented by Mike Willis of Pivotal Resources, and was attended by almost forty of the conference delegates. The conference was a great success and provoked detailed discussions after the talks given by experts in their fields, as well as in the breaks. The feedback from sponsors, speakers and delegates has been very encouraging.

Wednesday 13th April

Session 1 – Colorants & Dispersions
Session Chair – Philip Double, FFIC

Pigment dispersions and technology for aqueous inkjet inks
Rupert McIntyre,
Dispersions Research and Technology Group Leader
Fujifilm Imaging Colorants

Rupert McIntyre reviewed the science behind dispersion of particles and discussed the specific requirements for inkjet ink dispersions. One of the most important factors to consider is stability – the dispersion needs to be highly robust as this is the foundation of the ink. Pigment loading was another consideration that was discussed - if you have high loading this has advantages for inks including high colour but gives an additional challenge for stability. The other key requirements are durability of the final image, purity and bio-control. Purity includes keeping oversize particles numbers as low as possible (which requires particle counting instruments, not particle size distribution measurements), and the absence of impurities such as polyvalent cations and residual monomers. Bacterial growth in aqueous dispersions is a real problem as they contain a large surface area, water and have a mild pH. Care needs to be taken at all manufacturing stages to control this.

Organic pigments for sensitive inkjet printing applications
Dr Stéphane Biry
Senior Marketing Manager Digital Printing

Stéphane Biry discussed the digital food packaging printing regulatory landscape and how the migration of ink components impacts this. Food packaging represents approximately 50% of the global consumer packaging market and at least 75% of packaging is printed. Food packaging is considered a sensitive application because often the packaging is in direct contact with food, which can pose potential health issues and is therefore subject to extensive regulations. Other sensitive applications include toys, direct food printing, construction materials, medical devices and pharmaceutical and cosmetics packaging. There are a number of food contact regulations such as FDA 21 CFR, EU GMP, Swiss Ordinance, German Ink Ordinance draft and many others. Stéphane then discussed ink migration and its impact. All printing inks have the potential to migrate but selecting low-migratory/non-migratory components can help – ultimate responsibility is with the brands but all stages of the value chain have the chance to make a difference. Using barrier substrates like glass or metal can eliminate migration through layers but set-off problems remain. The biggest problems with food contamination have come from UV-cure photoinitiators, but components in organic pigments are also a potential problem. Primary Aromatic Amines (PAA) used in colorant synthesis are very toxic and there are 22 PAAs that are CMR substances (those posing a carcinogenic, mutagenic or reproductive risk) and not allowed in contact with food. Stéphane discussed BASF pigments that does not use PAAs in their synthesis, also announced a new analytical testing method for PAA in colorants which is being released as an industry-wide protocol.

Commercial and industrial inkjet dispersions - a key ingredient for high quality inkjet fluids
Joe Ward
Vice President, Marketing
RJA Dispersions

Joe Ward explained the requirement for digital printing colorant dispersions: they should not fade, settle or clog printhead nozzles and should have the right viscosity, rheology and particle size and stability while being easily incorporated into jettable fluids. He described the processes that are used to create stable dispersions and prevent agglomeration, including electrostatic and steric stabilisation, and also discussed self-dispersed technology using surface-modified pigments and core-shell approaches. The regulatory environment for dispersions was also reviewed. The milling process used to create fine particles was detailed, with the requirements for sharply-peaked distribution with zero large particles being key for reliable dispersions in digital printing applications. Techniques for measuring particle size and their usefulness for dispersion manufacturing were also reviewed.

Advances in colorant chemistry for inkjet printing
Takashi Yoneda
Senior Chemist, Dyestuff Synthesis
Nippon Kayaku

Takashi Yoneda compared the differences between dyes and pigments and their relative strengths and weaknesses. Yoneda-san then focused on the techniques used at Nippon Kayaku for dyestuff development and manufacture. Typical inkjet dyes for consumer printing are direct dyes or acid dyes. Cyan dyes often suffer from oxidative fading in photo applications giving an orange-like discoloration. This fading was reduced using analogues of direct blue 199pthalocyanine-based dyes containing sulfamoyl groups. These groups improve light fastness but impact solubility, so soluble versions of the groups have been developed. Magenta dyes also show fading leading to a green discoloration in prints, which can also be addressed with new functional groups. New direct black dyes have also been developed by NK, giving a neutral black and low fade.

Digital metallic inks - challenges, progress and applications
Volker Jordan
Head of Formulation Technology - Digital Printing

Volker Jordan explained the challenges of developing metallic pigment inks. The optical properties of metallic pigments such as colour, brilliance and coverage are influenced by the metal alloy used, wetting behavior, particle size, shape and orientation. The metallic effect is dependent on the proportion of reflection to scattering – ideally reflection dominates but this calls for relatively large flakes uniformly oriented in the final image. This is a challenge both in the ink, as large particles are more difficult to disperse reliably, and on the surface, where case needs to be taken to allow the flakes to lie as flat as possible. The positioning of the flakes within the image is also important – if the flakes lie close to the surface, the image is highly metallic but rub resistance is lower compared with a more uniform distribution which trades lower metallic effect for better rub resistance and adhesion. Eckart have released solvent, standard UV cure and LED cure inks with special processes used to create suitable metallic particles. A variety of effects are possible on substrates like polymers, textiles and leather.

If you missed the event, you can order conference proceedings, including full audio from the event, by going to our Order Proceedings page.

Tim Phillips & Kirsty Inman, IMI Europe and Phil Double, FFIC