How to improve print quality in four steps

1. Select the right line count

The screen specification of an anilox roll

is an important consideration which will

impact print quality. The objective is to

use always the finest anilox screen count

possible, providing we can achieve the

required color densities.

Higher line counts will provide a finer ink

distribution, which will be critical during the

printing process. The line count determines

the total number of ink dots that will be

transferred to the plate. Higher line counts

place more cells closer together. Smaller

dots will dry faster, producing less dot gain,

which will offer better image clarity in

process jobs.

When selecting a line count for a process

job, the rule of thumb is to specify the line

count at least five times the plate screen.

This ratio allows the cell walls to adequately

support the dot and keeps the dot from

dipping into the cells.

Line count is chosen in correlation with

cell volume. For example, if for printing

solids a volume of 8 cm3/m2 is required,

the line count will be approximately

400 LPI. Please consult Herzpack Anilox

Technology’s volume chart to select the

optimum volume for the chosen line count.

The only downside with fine line counts

is the cell size is reduced, becoming more

challenging to deliver an adequate cell

volume for achieving the correct color

densities.

2. Maintain a consistent volume

Maintaining a consistent ink volume is

critical to color reproduction, and the anilox engraving specifications are key

to controlling ink film thickness on the

printing plate.

Ink film thickness is the volume of ink

that transfers to the printing plates and is

what determines color strength and print

quality. The strongest, thinnest film of ink

(while maintaining color density) always

prints best. Without enough volume, the

color prints weakly. On the other hand, an

overload of ink results in dirty print or too

much dot gain.

In order to find that sweet spot in the

amount of ink transferred to the substrate,

a number of things must be addressed,

like the type and viscosity of the ink,

the type of printing plates used, and the

types of substrates. However, in order to

systematically control the color and print

quality, the consistency of the engraving is

paramount.

One main factor that will affect the ink

transfer from the anilox cells is the cell

shape and engraving geometry. In order

to ensure a consistent ink film thickness,

the anilox specification should be within a

depth-to-opening ratio of approximately 30

percent. This will ensure a good, effective

ink release from the anilox cells to the plate.

“In order to find

that sweet spot in

the amount of ink

transferred to the

substrate, a number

of things must be

addressed”

Depth-to-opening ratio is defined by how

shallow or deep the cells on an anilox roll

are. For example, if a cell is 30-μ. deep and

100-μ. wide, its depth-to-opening ratio is

30 percent. On average, a 30 percent depth

to-opening ratio may transfer 20 percent of

this volume to the web. If the same cell is

40-μ. deep, its depth-to-opening ratio is 40

percent. This cell may transfer 18 percent of

what it holds to the web.

In other words, at a given line count,

the deeper a cell gets, the percentage of

ink transferred to the plate reduces. When

possible, it is recommended to use depth

to-opening ratios in the 30 percent to 35

percent range.

3. Cell geometry

How does one determine which engraving

to use on the anilox roll? As shown in the

chart, it is not solely the volume of the

anilox roll. Rather, it is a function of the cell

geometry on the anilox roll that dictates

exactly how much ink transfers to the

printing plate. This ink film thickness should

be the focus when selecting an engraving.

The chart is an example in which the same

ink film thickness was achieved using two

different volumes. The result? Both the

color strength and dot gain were almost

identical.

How can a 3.5 volume produce almost

identical results when compared to a 3.0

volume? The 1,000 is a deeper engraving

4. Adequate maintenance

The key to ensuring maximum performance

from anilox rolls is implementing a

preventative maintenance program.

This means not only ensuring rolls are

thoroughly cleaned after each use, but also

tracking their essential data points.

Anilox cleanliness is critical because dirty

or clogged cells can degrade performance

by reducing cell volume and causing uneven

appearance or random patterns in the print

or coating.

In order to ensure reproducible results,

regular cleaning is essential. Adequate

cleaning and maintenance will preserve the

original characteristics of your Anilox rollers

and prolong their life.

It is imperative that when an anilox

roll is returned to storage that any chips

or scoring lines have been documented.

The volume should be measured, and the

data should be captured so the prepress

department knows that each roll is 100

percent ready to run the next job.

By taking the proper precautionary

measures and maintaining a strict cleaning

regimen, converters are likely to see vast

improvements in how long their anilox rolls

remain viable.