Flexographic (aka flexo) printing quality rivals the quality of both offset and gravure. Is this the first time you heard this? Probably not! If you are reading this, you are likely aware flexo is the No. 1 print method for flexible packaging in both the United States and Europe. The evolution of flexo from a somewhat viable option to the No. 1 choice is multifaceted with advancements across the entire printing process.

One major factor is that flexo printers are optimizing their processes with flat-top dot photopolymer printing plate solutions. It’s been said, to do a job correctly, first you must have the right tools. In today’s flexo printing market, having the right plate (the tool) can make the job easier, more consistent, and ultimately more profitable.

Flat-Top Dots
The packaging market consists of four major market segments: flexible, tag and label, folding carton, and corrugated. MacDermid Graphics Solutions (MGS) has an out-of-the-box, flat-top dot solution for all markets called LUX In-The-Plate (ITP). Why use a flat-top dot plate? Flat-top dots offer increased impression latitude, print consistency, and faster press start-ups. In addition, with MGS’s LUX ITP technology, you get near 1:1 imaging with an optimized dot structure for better wear characteristics.

What does that mean for you? With the bump curve greatly minimized, that means you have now opened up your tonal range to print a wider range. This can give you cleaner vignettes, better highlight definition, or allow you to hit those “impossible” spot colors with process color inks. Since launching LUX ITP in 2016, MGS customers tell us these plates “even-out” the skill level of their press operators. In other words, they don’t have to worry about having only their best operators run critical jobs that would normally require a very light impression set.

The Choices
OK, you want the best print, right? Well…you need the best plate. But which plate do I choose and where do I start? Begin with plate durometer. The plate durometer impacts the print job. Each market segment has its own general plate durometer requirement due to the substrate being used:

• Soft (~ 20-30 Shore A) durometer for corrugated
• Medium (~ 50 Shore A) durometer for folding carton and narrow web
• Hard (~60 Shore A) durometer for flexibles, usually wide web film applications

MacDermid measures Shore A using the ASTM standard by measuring the photopolymer stacked to 0.250” thickness without a polyester backing, giving us the polymer’s true Shore A number. We can also measure the effective plate durometer using the same instrument, providing a relative measurement of the plate durometer at the specific gauge at which it will be printed. For example, our LUX ITP 60 plate, a 60 Shore A at a 0.250” stack, measures 68 durometer on an 0.067” plate. The durometer is an important number to know when choosing your plate, and is a factor to consider for each market segment.

The Markets
The corrugated market requires an extremely soft plate. This requirement is driven by the construction of the print media itself – balancing print performance with packaging strength requirements. On the print side, corrugated printers require a plate that will be soft enough to cover recycled Kraft board, but not too soft that it’s a detriment to printing a continuous tone image. By using a softer durometer, the plate can conform to the texture of the substrate and print a smoother solid without crushing the structure of the corrugated board.

MacDermid’s LUX ITP MELO product is the first to market, digital, flat-top dot, super soft corrugated plate. With a 25 durometer Shore A at 0.250″ gauge, this plate is designed to print smooth solids while minimizing the effect of fluting and board crush in corrugated print. LUX ITP MELO’s super soft shore A and dot profile are the key attributes to minimizing board crush and fluting.

Tag and label and folding carton printers have traditionally used medium durometer plates. This requirement was partially driven by the need to wrap a plate around a very small cylinder. The important part… the plate needs to wrap and stay in place for an extended period. Certainly, the mounting tape plays a part in keeping the plate down on the cylinder, but more on tape later. Printing plates for this market print clean, high-quality graphics for long periods of time.

MacDermid engineered LUX ITP M with these requirements in mind. LUX ITP M features very low tack which makes dust and debris, present in some paper stocks, no longer a factor. The durometer of LUX ITP M is a little firmer than most medium durometer plates so it can be optimized for wide web applications as well, but it retains the high flexibility required for the smaller print cylinders.

For flexible film printing applications, most printers use a harder durometer plate. These plates typically start off around 60 shore A. Again, this measurement is taken at 0.250” thickness and without a polyester backing. Having said that, there are several printers today using plates that have an effective durometer in the low 70s or even higher. Most wide web printers need a plate that is harder to ensure the very best dot reproduction on their substrates. A plate that is too soft for the application can print with slur or excessive dot gain. LUX ITP 60 was the first flat-top dot in-the-plate product on the market and subsequently won the FTA Technical Innovation Award in 2016. LUX ITP 60 provides outstanding print quality and consistency, minus any extra steps needed to achieve flat-top dots.

Flexible film printing struggled to attain a balance of low dot gain with good solid ink density and coverage. Cap technology was the solution. A cap is a micro-rough layer on top of the photopolymer printing plate that aids in the transfer of ink onto the substrate. Think of it as something like sandpaper–with peaks, valleys, and crevasses that allow more ink to be picked up by the plate. This allows the best of both worlds – a hard plate that gives you good dot reproduction with good ink transfer. Then came surface screening technologies allowing you to build the microcells in the image file, becoming favorable over capped plates.

While prepress screening technologies are great, they require a high degree of process control on your press. The skills required, combined with the decrease in prepress specialists, means the simplicity of cap technology is desirable. And now…The Cap is Back! The introduction of new capped plates with inherent flat-top dots like our LUX ITP EPIC plate, provide the print consistency and high solid ink density needed to produce the finest detail graphics on flexible film.

About that tape…
It’s important to understand that the durometer of the plate shifts as the plate gets thinner because there is less material and more influence from the polyester backing. The effective durometer is also influenced by what is under the plate when it is mounted…the mounting tape. It is important to work with your plate and tape supplier to fully understand the plate/tape relationship specific to your printing environment.

Knowing what we know about plate gauge and substrates, it’s obvious why optimizing the entire plate/tape package is an essential part of making sure you have the right tools for the job. One such property – DUROMETER – is an important element to consider during the optimization process.

The Takeaway
What did you learn? Choosing the right plate for your printing process is important for your solid ink density, ink coverage and dot reproduction. A super hard plate has low dot gain, making it ideal for your highlight dots but poor for your solids. In contrast, a super soft plate is great for your solid ink coverage but poor for your highlights, which will result in high dot gain because of the compressibility of the photopolymer dot. As a printer, you must determine what aspect of your printed work is most important to you. Do you print mainly solids and line work, where a softer plate would be beneficial, or do you print high-end process color graphics that would benefit from low dot gain? In today’s flexographic market, starting with the right plate can make the job easier, more consistent, and ultimately more profitable.

About the author: Jason Cagle is an account manager at MacDermid Graphics Solutions. He is an FTA FIRST implementation specialist and was recently honored as the 2018 recipient of the FTA Presidents Award. He based this article on “The Right Plate for the Job in the Flat-Top Dot World,” by Ronnie Scogin, applications development specialist at MacDermid Graphics Solutions. Ronnie has more than 30 years of experience relating to flexible packaging, with the last 13 years spent at MacDermid.