Ink and Ink Dispensers
Ink Thick and the Thin By Tom Kerchiss, chairman of RK Print Coat Instruments Ltd
setting and impression settings are more forgiving because there is less ink to skew the separation. The smaller amount of ink on the tip of the dot is also more diffi cult to distort.
A high line count anilox roller is an option; lower volume anilox uses a smaller cell with a shallower engraving depth. Shallower engraving depths hold less ink, which in turn produces a thinner ink fi lm.
C
onsistent results in fl exography are, to some degree, dependent upon how much ink, whether thick or thin, is laid down on the plate and on the substrate. Anilox, doctor blades and plate mounting tapes cannot be left out of the fl exo quality equation; neither can devices that enable colour, text and graphics to be monitored and adjustments made.
Given the right circumstances, there are quality and performance advantages to be gained when using the minimal amount of ink. For example, if a press has less than perfect dryers, applying less ink speeds drying. Speedier drying prevents bottlenecks and reduces the risk that product shipment or additional converting processes are delayed because of wet ink. Wet or insuffi ciently dried ink can produce many problems. Ink that is still wet may lift from the substrate and, depending on press set up, may transfer to the plate in the next deck. As the transferred ink builds up, the printed image will become progressively dirtier.
With the smooth and controlled lay down of a thinner ink fi lm, using the appropriate anilox roll and doctor blade not only do large solids appear even and consistent, but also the rest of the line work improves as well. Type prints sharper because the controlled ink layer on the surface of the plate does not build up on the shoulders as readily. Reverse type benefi ts the most; less ink allows for smaller point sizes to be
reproduced with less risk of fi ll-in. The aim of the fl exo printer is to have as many sizes of dots as possible in order to reproduce an image with depth and visual acuity. By printing smaller, low percentage dots the printer is able to reproduce lighter or more defi ned highlight areas. In addition, when a high percentage of dots are open, there is better shadow defi nition. By laying down a thinner ink fi lm, there is less variability and a reduced risk of quality problems arising. There is more latitude in plate pressure
Since inks are primarily used for their communicative, protective and decorative attributes, great importance is given over to the subject of colour communication. Typically colour variability is defi ned as the Delta E of the inks when measured on a spectrophotometer. A Delta E between one and two is generally acceptable, but there are applications where the Delta E must be kept lower. In order to meet colour targets, colour matching capabilities must be precise and there must be good ink room to press correlation. Printers want colour matches and targets that they can actually print.
There are many variables that aff ect colour reproduction; the absorptivity of the stock not only varies among stocks even within the same category, but also from batch to batch within the same stock. This can aff ect the gloss of the ink fi lm by letting more or less of the vehicle portion of the ink fi lm to penetrate into the stock. The more the vehicle penetrates into the stock, the less varnish there is available for the top of the printed ink fi lm, which means that gloss will be less.
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October 2024
www.convertermag.com
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