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When looking at the
pad printing equipment market over the past few years, it is apparent that the
biggest change in equipment design and implementation has been the widespread
use of sealed ink cup systems over open inkwell doctor blade systems. A sealed
ink cup system is essentially and inverted cup that is filled with ink and uses
the sharp rim of the cup as a printing plate wiping system. As this system
floods and doctors (wipes) a printing plate in the same motion, solvent
evaporation and ink viscosity changes are much more limited than with doctor
blade systems, making the sealed ink cup printing process significantly more
predictable and manageable.
In the US marketplace
sealed cup systems have dominated new equipment purchases for a number of
years. This article discusses the types and applications of sealed ink cups and
advantages of ceramic doctoring rings.
Nearly all sealed ink
cup types can be broken into two categories, magnetic or non-magnetic. Both cup
styles, when integrated into the pad printing machine yield excellent results
for clean, properly doctored printing plates.
A magnetic ink cup is
basically “self-doctoring unit". With its extremely powerful magnets, it has
all the necessary down-force to clean the plate requiring the machine to simply
pull it back and forth. The magnetic ink cup generally has found its strength
in multi-color applications because the equipment can generally be of simple
construction and the multi-color pad printer more cost effective.
Non-magnetic ink cups
are designed to have the pressure applied by the pad printing machine to an
outer flange or centering hole in the cup.
The pressure is applied by a spring-loaded system geared for one ink cup
assembly. The spring-loaded system is compact and very effective, but is not as
simple to deploy on a multi-color machines.
The non-magnetic cups seem to have their niche in compact or high speed
machine applications. In these systems, even at high speeds, the spring loaded
hold-down system keeps the ink cup firmly in place while the plate moves in and
out.
There has been much
debate about which ring material is best for doctoring printing plates. We
would guess that the marketplace is evenly divided between the carbide ring and
the new generation ceramic doctoring ring. Today, both carbide rings and
ceramic rings work extremely well. It is
our opinion however, that the ceramic doctoring ring offers some advantages.
One of the primary
advantages of the ceramic ring has a “self-lubricating" qualities that make I
work equally well on thin steel and thick steel and the softer polymer printing
plates. The carbide rings are generally fairly sharp and abrasive and will wear
a polymer plate material quickly. Another advantage of the ceramic doctoring
ring is that generally thicker, more robust and resistant to damage by during
handling. Most ceramic rings taper from the inside and outside diameter to a
“point" roughly .006" leaving plenty of material near the tip. Carbide rings, however, taper from the
outside diameter only to a “point" with a cross section of .003" leaving only a
minimum amount of material near the tip resulting in more damage during
operator handling. The combination of the ring profile and the brittle nature
of carbide make damage to rings fairly frequent during ordinary use.
In general, the
quality of the products in pad printing marketplace have become very high, so
regardless of the type of sealed ink cup or ring material you are bound to have
a highly successful experience.
Benjamin Adner is the
president of Inkcups Now, has over 18 years experience in the pad printing and
screen printing industry, and holds 3 major industry patents. His Mechanical
Engineering and MBA degrees are applied daily in his attempt to create new
products and find innovative solutions to pad printing and screen printing
issues. For more information on pad printing, visit Inkcups Now at
http://www.inkcups.com
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