DIRECT LASER ENGRAVING BASICS, BENEFITS, FUTURE BUSINESS
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.
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.
