Home' FLEXO Magazine : April 2017 Contents 112 FLEXO | APRIL 2017
One of the most vulnerable times for plates to be damaged is when
putting print cylinders in and taking them out of the press. Often in
wide web central impression (CI) applications, the drain from the
ink pans comes in close contact with the mounted printed cylinder,
thus extreme caution should be taken. While it is not always feasible
to block all UV light in a pressroom, one area that can be addressed
is between color lighting that comes in very close contact with the
A major cause of premature wear is overimpression. Setting final ink
and impression settings at press speed will help in achieving the kiss
impression needed to maximize plate life. To get the most out of your
plates, do not excessively “squeeze” them to the anilox or substrate.
Excessive anilox to plate or plate to substrate impression can cause
wear on the lead edges, as well as abrasion, scuffing and stress crack-
ing. Not coming squarely into the proper impression can also damage
Understanding your ink system, extenders and cleaners is important
in maintaining not only plate life, but also color, viscosity and pH.
Some solvents are not compatible with photopolymer plates above
certain levels. Photopolymer plates are resistant only to certain types
and amounts of solvents used in inks and cleaners. Using the wrong
solvents, or using the right ones in high concentrations, can cause
swelling, shrinking, softening or cracking. Pure, 100 percent esters,
ketones and glycol ester should be avoided. However, some can be
considered as a co solvent with normal propyl alcohol at a much
While some consider the use of aliphatic/aromatic hydrocarbons
acceptable if used as a co solvent at 1 percent to 5 percent, it is a good
idea to avoid these altogether. Most alcohols/glycols are acceptable for
use with photopolymer plates, with a few exceptions which include
undiluted octyl, benzyl and methyl. When adjusting pH, most amines
are compatible, with the exception of morpholine. Highly pigmented,
water based inks can also accelerate plate wear if the ink is allowed to
dry on its surface or on the anilox roller. If the pH drops, it can cause
it to set up as a dry film that does not rewet. This dried film may flake
and form a grinding compound that can chew up the plates.
A swell test can be performed to determine the level of compatibility
of the solvent and the photopolymer plate:
• If swelling is less than 50-μ . and there is a loss of less than 3
Shore A, then the solvent would be considered resistant
• If swelling is 50-μ. to 80-μ. and there is a loss of 3 to 7 Shore A,
then the solvent would be considered conditionally resistant
• If swelling is greater than 80-μ . and there is a loss of greater than
7 Shore A, then the solvent would be considered non resistant
It is in the pressroom that ozone is often most apparent. Ozone (O3) is
a highly reactive gas compound composed of three atoms of oxygen.
Ozone occurs both in Earth’s upper atmosphere and at ground level.
In areas such as a pressroom, the most likely generators of ozone are
electrical motors and corona treaters. If you experience plate cracking
attributed to ozone, you can contact your plate maker or photopoly-
mer supplier and request an assessment of the area in question. Ozone
measuring devices measure in parts per billion.
CLEANING & REMOVAL
In order to maximize a plate’s life, it should be cleaned immediately
after the pressrun. Inks should not be allowed to dry on the surface,
since they may become difficult to remove and can lead to surface
damage from scrubbing or cracking when the plates are flexed.
Plates should be cleaned with a lint free cloth that is free of any harm-
ful debris, or a soft natural bristle brush to safely remove ink in screen
and process areas without damaging the highlight dots. Do not use
nylons to clean plates. The nylon material acts as a grater in fine high-
light dot areas. NP alcohol may be used sparingly to clean polymer
plates. However, plates should not be soaked in any cleaning solution.
Acetate should not be used to clean plates. However, if acetate is used
press side or for cleaning purposes, it should be used in a reduced
solution no greater than 20 percent.
Plates are to be completely dry before stacking and stored flat. Plates
should not be rubbed in order to dry. Blot or blow them dry, using a
lint free towel or cloth. Extreme care is required when demounting
plates. Some manufacturers supply demounting tools which assist in
the removal of the plate from the print cylinder. No sharp objects or
knives should be used, as they could damage the plate.
Starting at the edge of the mounted plate, slowly pull it from the
mounting tape while working your way across the print cylinder.
Once the plate has an exposed flap, grasp and peel it from the cylin-
der. If the mounting tape is aggressive or if adhesive transfers to the
back of the plate, a small amount of alcohol may be applied between
the stickyback and the plate back. Alcohol will assist in breaking down
the adhesive layer of the mounting tape.
Plate, sleeve and cylinder storage systems vary f rom converter to
converter. Regardless of the system used, minimal contact minimizes
damage, a suitable temperature for storage is required, and there must
be protection from UV light and ozone.
“The closer you can perform the main
exposure to the back exposure, the
better off you will be.
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