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|You are here: Home > Technique > Processes > Scientific report of the LGP2 > Printing processes > Study of the wettability and the transfer of new generation blanket ink||Update: March 21th 2007|
|Scientific report of the LGP2
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|Researchers of the LGP2 (EFPG, INPG, CNRS, CTP)
Documents taken from the
"Scientific Report of the Laboratory of Pulp and Paper Science and Graphic Arts - UMR 5518
Grenoble - France
January 2002-November 2005"
Éliane Rousset, Robert Catusse, Christophe Mercier, Jean-Luc Tourron
Quality is a very important factor in graphic communication.
A lot of parameters come into play such as the characteristics of the paper and ink
used as well as the transfer of the ink from the inking system to the substrate to be printed. In the
offset process, this transfer is done indirectly from the plate to the paper via the blanket.
This transfer has been studied as part of a study with the company Mac Dermid Graphic Arts.
The blanket is a rubber multimaterial. Its production involves many operations. It has two main functions:
The most used blankets are the compressible ones. Currently studies are in progress in order to improve this material. The blankets studied are called “new generation”. They have been modified so as to improve their characteristics and above all to simplify their production.Thanks to contact angle measurements their surface energy has been calculated. Their topography has been characterised by roughness measures. The transfer coefficient of ink for different substrates has completed the study. Correlations have been shown between distribution of the surface roughness, surface energy and ink transfer which have allowed a link to be established between the characteristics of these blankets and the way in which they were wetted or treated as well as the influence of the grafted surface.
Surface energies have been obtained by the large drop method using a device perfected in our laboratory.
In this case a simple measurement of the drop height is required.
The system used to measure the drop height, consists in a sensor with laser beam and photodiode
The surface roughness of each blanket as well as its profile have been calculated with a device Papermap from the company Cotec. The roughness values are directly obtained and completed by the evaluation of asymmetry and profile flatness factors.
On this image, the differences in colour represent variations in depth. In the case of the moulded grafted blanket, red colour strips could signal the effect of grafting [Figure 1].
|Figure 1 - Depth variations of moulded grafted blanket|
The quantity of transferred ink plotted against the quantity of ink on the
printing medium gives a straight line. The quantity of ink caught on the blanket
is represented by an abscissa at the origin of the straight line and the
ink transfer coefficient is represented by the slope.
This is true for “old generation” blankets. However, with the blankets tested,
which are much smoother, the straight line passes near the origin because
very little of the ink remains trapped. In order to characterise the influence
of the medium/substrate on ink transfer, tests have been carried out on
two papers : one glossy coated paper and mat coated paper. The quantity of ink transferred to the
blanket is similar for the two papers despite a very different BEKK smoothness. The difference obtained
between absorbent and non-absorbent media is much less for a non-grafted blanket.
In conclusion, the kind of medium to be printed has a bigger influence with a grafted than with a non-grafted blanket. It can be of interest to know on which kind of medium a printer works in order to make the best choice of blanket.
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