The quality found in flexographic printing today rivals both offset and gravure. There are many reasons for this, but one is that flexographic printers are now optimizing their processes more effectively with flat top dot plate solutions. Just like printing with traditional digital plates when optimizing one’s print process, the printing plate and the effects of durometer are factors that should be explored.
It’s been said that to do a job correctly, first you must have the right tools. In today’s flexographic printing market, having the right tool (plate) can make the job easier, more consistent and ultimately more profitable.
Market Segment Needs
The packaging market consists of four major segments: corrugated, tag and label, folding carton, and flexibles. Luckily, there are flat top dot solutions for each of these.
But first, why use a flat top dot plate? There are multiple reasons. One, flat top dots offer increased impression latitude and print consistency. They can provide near 1:1 imaging and an optimized dot structure, which gives better wear characteristics. Printers who use flat top dot plates have said they “even out” the skill level of press operators—In other words, they didn’t have to worry about having only their best operators run critical jobs that would normally require a very light impression set.
On the durometer front, each market segment has its own general plate durometer requirement based on the substrate being used and package requirements:
- Soft (~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 Graphics Solutions measures Shore A using the ASTM standard by measuring the photopolymer stacked to 0.250-in. thickness without a polyester backing—which gives us the polymer’s true Shore A number as referenced earlier. We can also measure the effective plate durometer using the same instrument, which provides us with a relative measurement of the plate durometer at the specific gauge it will be printed. For example, MacDermid’s 2016 Technical Innovation Award winner ITP60 plate—a 60 Shore A at a 0.250-in. stack—measures 68 durometer on a 0.067-in. plate.
Corrugated
Each market segment has its own set of challenges which require the use of different durometer plates. For example, the corrugated market requirements for an extremely soft plate are driven by the construction of the print media itself—balancing print performance with packaging strength needs.
On the print side, corrugated printers require a plate that will be soft enough to cover recycled kraft board but not so soft that it’s a detriment to printing a continuous tone image. By using a softer durometer, the plate is able to conform to the texture of the substrate and print a smoother solid without crushing the structure of the corrugated board.
Tag & Label, Folding Carton
Tag & label and folding carton printers have traditionally used a medium durometer plate. This requirement was partially driven by the need to wrap a very small plate around a very small cylinder and—here comes the important part—it needs to stay in place and not lift from that cylinder. Certainly, the mounting tape plays a part in keeping the plate down on the cylinder. However, the softer the plate is, the better drape or flexibility it has to properly lie down on the print cylinder and mounting tape.
Printing plates for these markets must also be capable of printing very high-quality graphics and have the capability to print cleanly for long periods of time.
Flexible Film
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-in. 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.
It’s important to understand the durometer of the plate shifts as the plate gets thinner because there is less material (with more influence from the polyester backing) and that the effective durometer is also influenced by what is under the plate when it is mounted.
In general, the mounting tape should be of a like modulus to the plate. In other words, a hard plate requires a firmer/harder density tape. The same general rule applies to other plates as well; for example, a soft plate requires a soft tape or carrier sheet and a medium durometer plate would generally require medium-density tape. Of course, these are generalities, but MacDermid always recommends optimizing the plate and mounting tape package in order to find the right combination that works for your application.
An Essential Component
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 not only a very important element to consider during the optimization process—it is also very easy to measure with many variations available.
About the Author: Ronnie Scogin is an applications development specialist with MacDermid Graphics Solutions. Ronnie has more than 30 years of experience relating to flexible packaging, with the last 13 years spent at MacDermid. Ronnie’s expertise includes proper plate selection and optimization, pressroom auditing and best practices, and plate and print defect troubleshooting. Prior to 2016, Ronnie was a valuable member of MacDermid’s Technical Applications group, working directly with customers in the field across all flexo markets.
MacDermid products referenced in this article include: for corrugated, Digital MAF (a 32 durometer Shore A at 0.250-in. gauge that is designed to print smooth solids while minimizing the effect of fluting in corrugated print); for tag and label and folding carton, LUX ITP M (a medium durometer LUX In-The-Plate solution, designed to be very low tack, so that dust and debris that are sometimes associated with some paper stocks are no longer a factor); and for flexible film, ITP60 (the first flat top dot In-The-Plate product to market and winner of a 2016 FTA Technical Innovation Award; it provides all the benefits of a LUX laminated hard durometer plate out of the box, like outstanding print quality and consistency). Learn more at graphics.macdermid.com.