Ink metering and transfer of ink remains critical for both line work and half-tone, and the printer can improve efficiency, quality of print (and repeatability) and ink lay-down while reducing costs of ink/usage.
There are two issues regarding (solvent-based ink) anilox selection.
Opacity and smooth lay-down of white ink: Until recently it was the norm to specify coarse screen ruling aniloxes (for whites and varnishes) so that the anilox could carry a high volume of ink without the cell walls collapsing over time – eg 80-100lpi at 12 to 14cm3 volume. However, the wide cell walls would show as ‘holes’ – one could see the pattern of the anilox – and ink lay-down would not be smooth. Whites could even seem ‘greyish’.
Through improved anilox manufacturing processes and the use of coatings, it’s now possible to produce a far smaller yet deeper cell and still achieve good ink release. Cell walls are very thin, allowing whites to be smoother, whiter, and have fewer pinholes. Today, an example of a white inking anilox would be a 150lpi screen, rather than the 80lpi screen ruling – yet still maintain 12 to 14cm3 volume.
Anilox volumes/viscosity: A printer needs quick and easy adjustments on the press, and this is achieved by positioning anilox selection and ink viscosity in the ‘middle’ of the spectrum. Ink viscosity must allow the press operator to control the actual transfer of ink to substrate, and to control half-tone dot gain. Highly viscous inks are prone to different drying speeds at variable ambient temperatures, reduced mechanical properties of the ink, and variable dot gain. Very thick inks do not transfer well, and lead to a myriad print problems. In my experience, ink of 25 to 26 seconds ZAHN 2 offers correct density, good and stable release, a ‘constant’ dot gain factor and good mechanical properties.
The anilox screen ruling and volume specification should be placed ‘middle of the road’. The printer doesn’t want to change anilox for every different job run on the press to achieve the desired print result. Slight adjustment of viscosity is preferable. Screen ruling of the anilox no longer dictates the volume it can carry, or is not as critical as before. In the past, to print 100lpi on the printing plate, a ratio of anilox to plate of 3,5 to 4:1 was specified but that’s no longer the case. Today, for instance, using a 360lpi anilox of 3,4cm3 volume, an anilox of 360l/cm can be specified, carrying the same volume of ink.
The new-age aniloxes come with different cell shapes, screen angles and volumes. Below is (in my subjective printer’s opinion) ‘middle of the range’ for ceramic aniloxes, round dot at 60° engraving angle.
A banded anilox test roller – different screens, volumes and cell shapes – is always a good exercise to perform before finalising anilox specification.