In the field of press printing, the majority of prints are done through the lithographic process. Lithographic inks are constituted of a vehicle composed of inks and oils, in which insoluble pigments are dispersed. Biobased offset ink carriers derived from vegetable oils are already in use, particularly in daily newspaper printing (coldset inks). However, pigments are generally petroleum-based. The aim of this thesis is to investigate the potential of biobased pigments to reduce the environmental footprint of printed materials. This thesis is funded by the Ministry of Culture, under the fund for the ecological transition of the press, and by CITEO. It is being carried out in partnership with Sun Chemical and Ecograf.
An experimental approach was adopted to select and study bio-based black and coloured pigments. Inks were formulated using these pigments and an ink vehicle supplied by the industrial partner. The pigments were chosen to match the colours used in four-colour printing (cyan, magenta, yellow and black). Most of the black pigments used are pyrolysed plant materials. As for the coloured pigments, they are derived from dye plants. The inks were formulated, characterised and printed in the laboratory. Based on the results obtained, modifications were made to the pigments and formulations to improve their performance. An industrial pilot trial campaign and de-inking tests were conducted using an experimental black ink. A study of the environmental footprint of bio-based pigments was carried out in parallel using the LCA (Life Cycle Assessment) method to evaluate their ecological benefits.
Analysis of the characteristics of biobased black pigments has identified several areas for improving the corresponding inks. In particular, particle size distribution and carbon content have a significant influence on the colourimetric properties of the inks. The pigments have been improved sufficiently to formulate legible inks, although they do not yet match the performance of industrial inks. Furthermore, the calculation of the carbon footprint of these biobased black pigments demonstrated their environmental benefits in the formulation of offset inks compared to industrial carbon blacks. However, despite attempts at optimisation, coloured pigments derived from dye plants did not yield satisfactory results: the colorimetric characteristics, particularly the optical density of the printed matter, are well below the desired performance levels. Furthermore, the LCA study showed that there is little or no environmental benefit to favouring biobased coloured pigments over current industrial pigments. The results obtained have contributed to increasing knowledge regarding the LCA of inks and biobased pigments. The methods developed pave the way for applications in inks for other printing processes.
