Page 90 - Training 2019

INTRODUCTION:

Who would ever have thought that the archaic Letter press process, that evolved into Flexography
would over a short span of time evolve not only as a contender and competitor to Gravure, but would
also infiltrate the Lithography process. This has only come about because of the ceramic anilox roller
and the chamber blade system…..the heart of the Modern Flexo process.

With all this said, we now need to look at what vital function an anilox roller plays in delivering the
correct amount to the substrate. Flexography evolved from Letter Press, where the lead type was
replaced with flexible moulded rubber plate, the ink from paste to liquid, and smooth metal Ink Roller
to a mechanical engraved Anilox Roller. Control of transfer was manipulated with pressure between
the metal “Anilox / Inking Roller” and the rubber fountain roller.

This was the first radical changes, but as the need for better quality print arose, so the changes took
place in plate making, ink technology and the Anilox Roller development.

The mechanical Anilox Roller probably first started at a low screen count of 100 to 120# (lines per inch)
then 150#, 180#, 200#, 220# and 250#. At this point in time, plate making improved to better quality
rubber, to rubber half tone, and to photo-polymer plates. Ink systems are also constantly evolving, we
now have solvent based, water based and UV inks. Next came 360# free flow for fine half tone work
and cells with channels for better ink release and transfer.

This has been a constant race between plate, ink and anilox technology. To constantly improve print
quality Anilox Rollers screen will be finer and finer and this is where ceramic has played a major roll,
because photo-polymer plate dots will get smaller while inks need to become more sophisticated.

So now that we understand the Flexo concept, how does this fit into Litho.

The principle of oil and water do not mix is the fundamental basis of Litho printing. The ink is oil based
and takes time to dry between operations. This meant there was a large floor space requirement to
allow pallets of printed sheets to dry between printing and finishing. This was a slow process, but
could be speeded up if off line varnishing was done. First this was with spirit and UV varnish and later
with water based coatings. In Litho there was also the radical need to improve production speeds and
turnaround times. The next development was to do inline coating with water based coatings.

The first inline coater used a steel roller and a rubber metering roller with warm air to dry the water
based coating. The big advantage was that the sheets were dry enough to go straight to finishing with
no waiting to dry. However, as machines got wider and faster new problems manifest themselves.
The inertia of the coating between the steel and rubber roller would allow more coating to be applied
in the centre. The next step to overcome this was to bow the steel base of the rubber roller and then
even go as far as grinding the rubber so that it was thicker in the centre. All this helped but was not
good enough.

So enter the ceramic roller and the chamber blade system. No matter what the press speed, you
would always apply a uniform layer of coating controlled by the cell volume and a doctor blade. Then
we have water based coatings that can also be problematic if not cleaned after use. The rule is, after
use, clean immediately to prevent costly downtime.

FLEXO IN LITHO TRAINING MANUAL 2
Updated - 24 June 2019