Narrow Web Plate Advancements: Reduce Stops, Get Better Print & Laydown, Streamline Workflows

Imagine building flat top dots directly into the plate, removing additional plate making steps, increasing production, alleviating dot gain, promoting longer runs, and achieving reliable color. Could that be game changing?

Of course it would. In reality, it is! Flat top dot technology is an ideal solution for tag and label printers/converters focused on quality and productivity. Going even further, building flat top dots directly into the plate combines the best of both worlds—the consistent, robust print performance of the flat top dot shape, and the efficient workflow and fine imaging capability of the digital plate.

Flat Top Dot Origins

To tell the story of inherently flat top dots in-the-plate (ITP) development, it’s important to position this technology within the evolution of flexo plates. Photopolymer plates were first introduced more than 50 years ago when they were designed to replace their rubber forefathers. The benefits were substantial improvements in:

• Productivity
• Imaging resolution
• Print capabilities

Rolling the calendar forward another 25 or so years, digital photopolymer plates were the next evolution. With this advancement, there were improvements in the imaging fidelity and print capability. Additionally, the digital workflow was more efficient and consistent than the analog process.

However, there was a price to pay, beyond the investment in the laser imager and higher plate cost: the digital plate making process produced very fine, bullet-shaped highlight dots (see Figure 1). Photopolymer producers stressed the advantage of having a sharpened dot that was slightly below print height. However, digital plates were more sensitive to impression and wear, as a result of the same bullet shape that delivered fine highlight dots.

In the traditional digital plate making process, dot formation is inhibited by the introduction of oxygen, thus creating bullet-shaped dots of varying heights, with mid tone dots more elevated from the floor of the plate than finer highlight dots. As a result, press operators often have to adjust and re-adjust the press in order to find optimal impression. This typically leads to several hundred feet of waste, both from the substrate and the ink.

But by preventing oxygen from entering into the plate making process, all dots come up to “type high,” meaning they are the same height across the plate. Now the press operator can get up to color quickly, without having to guess at the right impression. Perhaps more importantly, printers see an immediate savings in substrate and ink waste.

A simple lamination process, whereby a thin membrane is laminated to the digital plate after laser ablation and prior to main exposure, was developed by MacDermid Graphics Solutions to advance flexo printing through the optimization of the flexo dot profile. Introduced in 2010 as a first wave in the dot evolution program and dubbed “LUX,” this lamination step prevents oxygen from interacting with the surface of the uncured plate, thus inhibiting the curing process and creating a flat top dot.

Development & Integration

Through the chemistry optimization development phase, inherently flat top dots in the plate eliminated the lamination step, allowing it to be used in the existing plate making workflow without adding time or materials. ITP enabled plate makers to attain all the print benefits of the flat top dot profile, straight out of the box.

While the lamination step itself is a simple, quick, and still widely used method for producing flat top dots, ITP technology takes it further by removing the need for lamination entirely. A comparative example of the two dot shapes is shown in Figure 2.

Since the introduction of digital photopolymer plates, plate makers have been saddled with a gamut-robbing step—the bump curve. This is needed because digital photopolymer plates are exposed in air. The presence of oxygen inhibits the photopolymerization. The result is a bullet-shaped dot that is smaller than the hole in the mask.

The “bump” is the linear dot percentage that must be imaged into the mask in order to form a stable, 1 percent dot in the plate, at the specific linescreen used. As a result, there is a portion of the gamut that is lost—It is no longer available to the plate maker.

A digital plate produced using a process like ITP offers 1:1 mask-to-plate imaging capability, thus eliminating or greatly reducing the need for a bump curve.

The plate maker gains several imaging benefits:

• Increased tonal range and color gamut: With 1:1 imaging, the elimination or reduction of the bump curve returns portions of the gamut previously “lost” in the conventional digital plate making process
• Improved imaging consistency: When applied, the bump curve is dependent upon the linescreen and the imaging device. The bump for a 120 lpi job is not the same as a 150 lpi job. Secondly, even though a customer may have all the same type and model laser imagers, each one is slightly different and therefore the bump curve can vary. Lastly, the selection of the bump curve is a manual process that relies on human judgment
• Better quality control: Measuring the size of dots in a conventional digital plate is difficult. The bullet shape of the dot is the culprit. Using common tools like a plate and image analyzer or microscope can yield widely different results. A digital plate made using ITP technology has a flat top dot profile. As a result, reading tonal range using a plate and image analyzer or microscope is much more consistent, similar to analog plates

Customers who have printed using modern plate options agree the print pops. It simply looks better. Customers site:

• Faster press setup time: Users of flat top dot technologies state because the dots are at the same height as the solids, setting impressions (anilox and plate cylinder) happens more quickly
• Smoother vignettes: Especially when using hybrid screening, the ability to fade to zero improves (driven by usage of smaller dots)
• Improved solid ink density: Because of the sharpening of the edges associated with flat top dot chemistries and methodologies, the effectiveness of commercial screening options is greatly improved. This enhances the solid ink densities capable with digital plates, improving coverage and reducing mottle as a result

Where Are We Now?

Flexographic print quality today rivals both offset and gravure. There are many reasons for this, but one significant reason is flexographic printers are now optimizing their processes more effectively with the latest innovations in flat top dot plates, screening technology and UV-LED exposure

ITP advancements formulated with clean-plate technology are an important factor in the improvement of flexographic print. With these developments, all ink is transferred to the printed substrate and requires fewer press stops for plate cleaning which enables cleaner print and longer pressruns.

Advances in screening technologies are another key factor in the improvement of flexographic print quality. Screening is the translation from the continuous tone image to the printable image comprised of dots of various shapes and sizes. How we screen an image ultimately determines how faithfully that image is reproduced and how much of the original contrast, saturation and detail is preserved.

Synergies of ITP plate technology with emerging screening technologies have been designed with flat top dots in mind. Examples of advances in this area include Esko’s Crystal and Hamillroad’s Bellissima screening. Esko Crystal screens take advantage of flat top dot plates to form smaller printable structures within the plate to further improve those benefits of cleaner vignettes and increased color gamut. Bellissima is another screening technology that leverages flat top dot plate technology to push flexo screening to a higher level. Bellissima is digitally modulated stochastic screening that changes frequency and dot shape throughout the tone scale. With Bellissima screening and flat top dot plates, image contrast and fine details are reproduced faithfully to truly represent the original continuous tone image.

ITP plate technology, combined with the aforementioned advances, are suited for use in standard bank light or UV-LED light sources. With flat top dots and UV LED curing comes the ability to hold finer highlight dots. These fine highlight dots allow designers more flexibility in creating art that will pop off the shelf and catch the eye of the consumer. As you can see, inherently flat top technology is truly game changing. Now, brand owners are confident their products will stand out among the competition.