Details on DLE in Flexo Oct. 2017

Details on DLE

Direct Laser Engraving Basics, Benefits, Future Business

Brendan Pollard, Armin Senne & Adam Smrdel

At the start of this century, new laser technologies
emerged. YAG and diode lasers
started to become common in the plate
making process, at first only in mask ablation,
but later also for direct laser engraving (DLE).

Several engraving system manufacturers picked up on these technologies
and designed their systems around them. DLE technology for
flexo eliminates the costly outlay for multiple processing stages and
equipment commonly associated with more conventional photopolymer
sleeve/plate making technologies.

Flexographic engraving systems use single or multiple high-powered
CO2 lasers or fiber lasers to directly engrave continuous sleeves or
plates in a single step. The laser selectively ablates the non-print area
of an elastomer plate or sleeve to produce a print-ready surface without
the use of exposures or chemicals.

THE COMPOUNDS

Rubber has always played an important part in the flexo industry. Going
back to the last century, elastomer was mostly used in sleeve form
to print background colors in flexible packaging as well as printing on
tissue, wall paper and other materials for the decorative market.

There are several reasons elastomer did not really make its way
into the classic flexible packaging and label markets until recently.
Previously, engraved elastomer plates and sleeves were only suitable
for line work and relatively coarse linescreens up to 85 lpi. This had to
do with the limited elastomer compounds and the rudimentary laser
technology of the day.

A direct laser engraving workflow
involves fewer stages, reducing
the possibility for error. By
eliminating steps and variables,
we are eliminating failure points,
thus making the process more
consistent.

With the parallel development of high performance elastomers and
more advanced laser capabilities, new levels of quality are possible.
Current engraving technologies allow for resolutions of 4,000 dpi
and higher (i.e. 5,080 dpi in printed electronics applications). Screen
values of 200 lpi are used in everyday production throughout the
elastomer plate and sleeve producers around the world.

MATERIAL PROPERTIES

Today’s high-performance elastomers have more to offer than just improved
engraving capabilities. Most current elastomer printing forms
are made from a compound called EPDM (ethylene propylene diene
monomer). EPDM is a non-polar synthetic rubber compound that is
extremely resistant to UV light and ozone. Due to its polarity properties,
it also works very well with ketones, esters and alcohols, which
are polar substances, making it a perfect fit for flexographic printing,
not only with solvent-based, but also with UV and water-based ink systems.



The following fact can be used as a rule of thumb: Matching polarity
between ink and printing plate causes the former to migrate into the
latter, causing problems with swelling, premature wear and cracking.
Therefore, EPDM does not work with oil-based inks, gasoline and
aromatic hydro carbons (i.e. benzene); these substances are non-polar.
For printing applications using non-polar inks, such as offset printing,
the market uses NBR printing blankets (nitrile butadiene rubber),
which is an elastomer with polar characteristics.

Since EPDM-based printing forms do not swell with current flexo ink
systems and are extremely abrasion resistant, it makes them a good
choice in difficult printing environments, such as plastic cup, tube
and aluminum can printing, corrugated or nonwoven applications.
Surface properties, such as roughness and surface tension, but also
compressibility, are designed to neutralize the feeding characteristics,
which a lot of times are the cause of halo effects or mottling. The
compounds are also optimized to control ink pickup and release,
minimizing buildup.



ELASTOMER VS. POLYMER

Cost, perceived supply chain problems and limited inventories have
held back the use of elastomer sleeves in America, but new advances
in imaging and manufacturing are bringing their inherent advantages
to the attention of printers.

Elastomer sleeves are thicker and more durable, and can print two
to four times longer than polymer sleeves. This eliminates the need
to buy multiple plates or polymer sleeves for long runs and repeated,
abusive short runs that require many cleanings and press cylinder
mountings, and this leads to both cost savings and cost predictability
in the long run. A typical comment from printers who have switched
from polymer to elastomer sleeves is, “Elastomer usually costs less
than polymer, and we’re only buying one set instead of two—so the
savings are great, and our print results are more consistent.”

The following fact can be used as
a rule of thumb: Matching polarity
between ink and printing plate
causes the former to migrate into
the latter, causing problems with
swelling, premature wear and
cracking.

Further cost savings are realized because elastomer sleeves eliminate
the need to purchase expensive cushion adapters and replace them in
the future.

PRESSROOM PRODUCTIVITY

Flat plates have traditionally dominated the North American flexography
market. Even in the last several years, the limited amount of
cantilevered presses, the long lead time for sleeves and the perceived
high cost have hampered adoption. Printers are now demanding
ITR technology for several reasons, the most immediate of which is
efficiency.

ITR sleeves require no plate mounting stations, mounting material or
labor. This allows for quicker makeready. When mounted, digitally
engraved sleeves are aligned to each other during engraving (using
notches) for perfect registration. This leads to considerable savings
on labor, substrates and ink when getting up to color. With fewer
variables and a more uniform printing surface, press speeds can be
increased beyond what is capable with flat plates. Short run and repeat
jobs can be changed out quickly, and the increased durability of elastomer
sleeves allows for longer printruns.


Sarah Moravcik of Carey Color demonstrates loading of the elastomer sleeve on the Flexcel Direct System.


Since there are fewer things that can go wrong with sleeves during
the printing process—like undetected flat plate mounting issues, plate
lift, cylinder bounce, lack of uniformity, etc.—ITR can help eliminate
variables that lead to problems during printruns and cause press
downtime. While individual elastomer sleeves may be more expensive
than plates, increased productivity, combined with the elimination of
redundant plates, can actually lead to an overall cost savings over flat
plates.

The uniformity, consistency and registration of sleeves, combined
with the ink transference, density and resolution of digitally engraved
elastomers, allow for faster printing speeds with superior quality.
This allows printers to leverage new technologies to achieve ROI now
instead of later.

THE BENEFITS OF A DIGITAL WORKFLOW

A DLE workflow involves fewer stages, reducing the possibility of
error. By eliminating steps and variables, we are eliminating failure
points, thus making the process more consistent. With this process,
there is no essential ablation mask as with direct photopolymer laser
imaging.

DLE plates and sleeves are produced in a two-step process. First, the
non-printing areas are removed with a high-power laser imaging
system. A short, water-and-soap-based cleaning detergent wash-anddry
cycle follows, which is a lot less involved than the post-processing
stages for direct laser imaging or conventional flexo plate making
using photopolymer plates. Additionally, photopolymer washing
stages can often involve solvents harmful to workers and the environment;
laser engraving eliminates this. As sustainability becomes more
important to printers and brands, it’s essential to know that, from an
ecological point of view, there are no issues to be concerned of with
volatile organic compounds (VOC). The production of DLE printing
forms is completely free of solvent. Following that, the printing form
is ready to go on press.

The involvement of only two pieces of equipment and a true digital
output is especially appealing because the need for floor space is
greatly reduced. Taking a look into the future, it is fair to say flexo
printing form production will most likely move more toward the
printers, much as it did in the offset realm years ago. Data could be
sent straight to the printer, eliminating the shipment of plates. Remakes
are done quickly, with no auxiliary equipment needed.

FUTURE BUSINESS PROSPECTS

After this very broad overview of DLE basics, one question comes to
mind: If DLE is such an advanced technology offering this many benefits,
why is it not more popular? There is no simple answer to that.

DLE is facing the same issues as any other new technology, such as
digital plate making did in the beginning. These issues include slower
production speeds, machine and plate availability, initial investment
and so on. Just like in those days, development has to take place in
order to accommodate the market needs. However, over the last three
years, a lot of progress has been made. Engraving speeds have already
doubled and faster materials are now available.

Let’s look at DLE’s potential in specific markets:

  • Label printing: As label printers lean more and more toward UV
    inks, this will be one of the growth sectors for DLE technology.
    The smaller plate sizes, in combination with the material properties
    of the elastomer plates, will offer quite a few benefits when it
    comes to printing labels
  • Flexible packaging: With increasing production speeds,
    compressible plates that do not need cushion tape, coupled with
    all of the other benefits of elastomer compounds, the flexible
    packaging section of the flexo market has become increasingly
    accepting of laser-engraved elastomer printing forms. Faster
    press speeds and less “dirtying up” allow for more press uptime,
    adding to a significant cost savings
  • Corrugated printing: Pre-mounted, laser-engraved elastomer
    plates will result in an increase in print quality for corrugated.
    Eliminating registration issues and time-consuming mounting
    processes will attract corrugated printers to DLE. An increase
    in imaging speeds made possible with technologically improved
    engraving units with dual heads and four beams will make DLE
    even more appealing to this market sector
  • Specialty packaging: Dry offset printing (indirect flexo) for cups
    and cans has been lacking print quality due to the limitations of
    traditional plates, losing market share to IML (in-mold labeling),
    heat transfer and digital. Using DLE in this segment will certainly
    boost print quality, due to higher ink densities, higher linescreens
    and smoother vignettes (through the use of sub-surface
    dots in highlights). This segment is a classical UV ink application
    where elastomer’s natural material properties excel
  • Printed electronics: As this application becomes more mainstream,
    DLE plates will play a large role. With rotary screens
    being costly and limited in fine line detail, elastomer plates can
    provide a medium that will retain the intricacies while resisting
    the effects of abrasive inks and harsh solvents

 

IN CONCLUSION

The benefits of DLE will continue to grow as the technology evolves.
Faster lasers and improved elastomers will further drive printers to
the DLE process. The ecological advantages of DLE, driven by brands
and end users, may also determine how plates and sleeves will be
produced.


About the Authors: Brendan Pollard is managing director at Applied
Laser Engineering Ltd. Armin Senne is business manager, flexo at ContiTech.
Adam Smrdel is director of flexography at Carey Color Inc.

Pollard

Pollard

Senne

Senne

Smrdel

Smrdel

 

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