treatment is a way to alter surface adhesion properties
of the materials to be printed, making them more suitable
for the adhesion and coating of printing inks.
other words, corona treatment is a kind of electrical
discharge, which enhances surface adhesion properties
of the materials to be printed. Corona is produced
by discharge through high voltage and high frequency,
via grounded and inductive air jets of the corona
treatment equipment. The electric current does not
pass through the two air jets until voltage reaches
9,000~15,000V per square millimeter. Electric discharge
molecules burst out from the air jets carrying high-capacity
ions, and rush at the anode. Corona treatment is carried
out by ions intensively and powerfully burst out.
penetrate into surfaces of the materials to be printed
and destroy their molecular structures via electric
discharge, and further, oxidize and polarize the surfaces.
By corroding the surfaces, ion discharge enhances
surface adhesion level. However, to learn about the
physical features of corona treatment is not so important.
What we really need to learn is the treatment itself
and how corona treatment can help printing-related
industries with their work.
does corona treatment do?
What corona treatment really does is to change the
adhesion energy of film surfaces, enabling them to
better accept printing inks or meet coating needs.
Adhesion property measuring unit is "dyne."
To achieve effective ink adhesion, coating or varnishing,
surfaces of materials to be printed need to feature
higher than 10 dynes (of inks).
PE film surface features 31 dynes under normal circumstances.
However, if PE film needs to be printed with flexo
ink featuring 36 dynes, it should feature 46 dynes
to be in a better printing condition (36 dynes + 10
dynes). The gap between 31 dynes and 46 dynes exactly
requires corona treatment to fill up. We all know
that it is more difficult for flexo inks to be printed
on film than solvent-based ones. But why is it? It
is because the former features higher surface energy
than the latter. The surface energy of solvent-based
inks features 28 dynes, UV inks 32~34 dynes, while
that of flexo inks 36 dynes. That is to say, if solvent-based
inks are applied to film printing, the film surface
needs to be corona treated to achieve 38 dynes; or
46 dynes, while flexo inks are utilized. Partially
because of the development of flexo inks, corona treatment
is widely known today.
inks--water-based ink is the only solution
In the 1970s, only blown-film making plants have corona
treatment equipment. Firms in the packaging and printing
industries used to utilize solvent-based inks to print,
because film surface treatment is easy--the only thing
that needs to be done is to slightly raise film-surface
energy level during blown-film making--enabling the
adhesion of solvent-based inks, which feature low
surface energy level. However, in the 1980s, new environmental
protection treaties were established, and have since
strongly impacted upon the packaging and printing
industries. Environment protectionists worry about
how solvent volatilization may affect the atmospheric
boundary layer, not to mention affecting human lives
and the living environments. That was the time when
flexo inks were developed and produced to meet the
wide-web printing industry is the one who suffers
the impact the most in the field due to its utilization
of high-volatilization solvent-based inks; and the
first one as well to use flexo inks in plastic-film
printing. This helps advance technologies in terms
of inks, pattern rollers, ink transfer methods, pressure
rollers, and rapid drying systems, and has greatly
improved the environment for flexo-ink printing. The
improvement has also played an essential part in the
exploitation of corona treatment, as well as the change
of flexo-ink properties and materials for printing.
blown film is corona treated, the surface energy level
drops along with time in conveyance and storage, and
thus will not be able to meet requirements for flexo-ink
printing as much as before, and what's worse, making
high-speed printing and tiny-printing-dot transferring
very difficult. This is why firms in the printing
industry need to have corona treating machines.
the narrow-web printing industry also has a tendency
to use flexo inks for printing, because it has been
confronted with concerns from the environmental protection
organizations, occupational safety organizations,
and blue-collar health organizations. Paper tags and
labels need no corona treatment before printing. Unlike
plastic film, paper has no adhesion problems in flexo-ink
printing. However, the use of plastic film has obviously
been increasing among companies in such industries
as aerospace, in-mold tag and label forming, as well
as packaging. The narrow-web printing industry needs
to face the change as well-to print on plastic film,
with flexo inks. They have two options; to either
use high-price plastic lamination film, or to add
a corona treating machine to their printing lines
for corona treatment. Corona treatment is absolutely
necessary when it comes to printing with UV or EB
inks. Featuring high-energy surfaces, UV and EB inks
require high-speed printing, and corona treatment
is the key to achieving instant ink transferring and
drying, without causing pasty ink, ink flowing, and
half tone problems. It's not hard for us to find out
now why corona treatment has become so popular in
the packaging and printing industries.
Needs Corona Treatment?
Using flexo or UV inks instead of solvent-based ones
to avoid environmental pollution is a must today for
the printing and packaging industries. This has made
corona treatment even more indispensable than before.
Corona treatment is now widely applied, to plastic
sheets, metallic foils (including tin foils), etc.
in film lamination and plastic sheet mounting. A great
number of film-material manufacturers have corona
treatment equipment, because they need to do surface
treatment on materials to be printed for downstream
collaborators. Some of them also need to take care
of their own surface treatment business, such as destroying
surface-layer fibers of paper to allow it to receive
thin and smooth lamination of film (or i.e. film lamination
for aluminum foil), and to lower production costs.
Potentials and opportunities for corona treatment
have been welling out like springs and are never going
Corona treatment equipment has been improved in terms
of dimensions, efficiency, and capacity, as well as
treatment speeds and standards, in order to meet the
needs for in-line operation; and has also been innovated
in various ways to correspond to the demand of various
types of materials for printing. As a result, corona
treatment has become so sophisticated. Since the design
of corona treatment equipment can be affected by a
lot of factors, manufacturers are seeking to build
a standard model to meet all demands. However, customers
love only what meets their individual needs. To achieve
this, we at Chaang Horng are willing to invest on
corona treatment equipment R&D, and to innovate
the equipment both technologically and in terms of
assembly. Basically, corona treatment equipment is
available in three types, including conventional models,
models with exterior-mounted rolls, and three-dimensional
operating models. These are all designed to better
meet myriad printing requirements.
will the industry do in the future?
We believe what the industry will do in the future
is to emphasize on enhancing treatment speed without
damaging film surfaces. In fact, up to the present,
corona treatment has been fully exploited. We believe
there is no need for manufacturers to worry about
whatever new or different machine models competitors
will develop. Everyone in the field is challenged
with new technologies. We are proud that what Chaang-Horng
has accomplished in recent years is more than just
changing the machine appearance, but has developed
innovative and practical models.
fact, the use of flexo inks instead of solvent-based
inks has resulted in the intensive utilization of
corona treatment equipment in recent years. Ozone
produced by such a large number of corona treatment
machines is everywhere, which might have become another
environmental pollution problem. Maybe, in the early
'90s, corona treatment machinery was one of the tools
serving for competition, but now, it is only a basic
tool-a necessity that leads to the close cooperation
relationships between buyers and suppliers.