Throughout my time in the flexo market I have continuously been involved in research, training, troubleshooting, and projects to revolutionize the industry. Sometimes the results are small, sometimes big, sometimes accepted, but most often resisted. Most often the answer when I ask “Why do you do that?” is “because we always have!”
After a while you get into the same habits, and without realizing it you end up in the same mode of “that’s normal for flexo” and accepting some things that you really should not. We all do it! One example that comes to mind is “I have to choose between good highlights or good solids, I can’t have both!” This comes from the typical pinholed nature of the solids in flexo and the four main actions that people take to address it:
- Increase the amount of ink used with higher anilox roll volumes
- Increase the ink strength with more pigment
- Apply more impression pressure from the plate to the substrate
- Separate the screens (highlights) and solids onto two separate plates for that one color
However, when we look at each of these four “normal” actions in flexo, because of the need to choose between highlights and solids, we see the true results:
1. MORE INK! Adding more ink does not eliminate the pinholes in the solid, but instead it applies larger ridges of ink to the substrate surface. More ink means more raw materials, more solvent to remove in drying; more drying means more energy as heat. More dryer energy often means that there is a need to slow the press down to achieve this, resulting in lost productivity. These are all “normal” actions in flexo, resulting in more raw materials, more energy, higher costs, and reduced productivity.
Other issues with using more ink are that it tends to cause more dirty print, which causes more stops to clean the plates, and increases the risk of damaging the plates. This is a cost in time, productivity, and materials, but results in inconsistent print quality, and often negatively impacts subsequent processes such as lamination and slitting/conversion when the materials need to be stripped out. A common accepted “normal” action to reduce the risk of dirty print is to reduce the applied resolution, as LPI, making the minimum dots bigger, decreasing image quality capabilities.
2. MORE PIGMENT! Pigment is the component of the ink that provides the color we are looking for, and the theory is to use more pigment for more color. But when the ink is applied in ridges separated by pinholes, the effect and value are minimized. The best way to get the strongest and cleanest color is a thin even layer of pigment with no pinholes, more like what we traditionally see in gravure printing! The light then reflects more evenly, giving a cleaner, brighter, and stronger color.
Pigment is one of the most expensive, if not the most expensive, components in the ink, so adding more increases the costs significantly. Also if you keep adding pigment, density goes up until it reaches a point at which it interferes with the ink flow and can cause the density to drop. Most flexo inks are pigmented to the maximum, often beyond the optimum value for efficient printing. Ink flow is a critical factor, especially as press speeds increase, and poor ink flow will result in ink starvation and poor solids.
This can also cause increased dirty print in a similar way to more ink volume in the first action, with similar solutions to address it, resulting in higher costs, lower productivity, and lower image quality!
3. MORE IMPRESSION PRESSURE! This is something that every flexo printer in the world seems to know—that when you apply more impression pressure from the plate to the substrate, the density goes up!
When you ask why, not many can explain it to you, but they know it just works! The explanation for this is actually very simple—the ink is applied in ridges separated by pinholes or voids; and as you apply more pressure on the top of the ridge, the ink is squashed sideways, filling the voids and increasing the ink coverage, and increasing the density achieved!
Image 1: Typical Flexo Solid – showing the ridges of ink and pinholes
Unfortunately most also work on the principle that “If a little more impression pressure is good, then a lot more must be better.” This results in over impression, and that introduces a whole new set of issues.
Over impression causes excess dot gain in the highlights, accelerated plate wear in the highlights, and ink build up for dirty print. Although true for flat top and round top dots, the issues are particularly true for the round top dots of traditional digital LAMS (Laser Ablative Mask System), with the very small surface area being very sensitive to the pressure, growing rapidly, and causing excess heat and friction to wear the smallest dots. This accelerated wear, along with impression sensitivity of traditional LAMS plates, causes greater operator sensitivity and inconsistency in setup and through the run.
Over impression also tends to drive the ink off the smaller dots to the edges more, causing ink build up, resulting in dirty print. This then means more stops to clean the plates and that increases the risks of plate damage. Increasing the minimum dot size can help—with a lower LPI for the image, larger dots are less sensitive, tend to be flatter on top, and distribute the impression better. But doing this is a clear sign of accepting that this is normal to compromise the highlights to improve the solids.
4. SPLIT SOLIDS & SCREENS! This is really a sign of having to throw in the towel and accept that instead of one or the other you need to get the best of both worlds. This is a normal action with traditional LAMS plates with their rounded tops, and less often with the digital flat top dot solutions. This means more prepress—two plates, two mounting tapes, two inks, two print stations to setup, two driers to run, etc. Basically more materials, more energy, so more costs. One thing in its favor is that doing this means the plate suffers less from ink starvation and drying issues, and often runs easier and faster at times with traditional LAMS plates.
These four actions are “normal” and accepted as necessary throughout flexo, and in the past they often were needed. Today however this is not true.
The micro plate surface texturizations designed to break up the pattern that causes the pinholing in the ink transfer—like DigiCap NX introduced by Kodak in 2010, which minimizes pinholing without needing more impression pressure—has resulted in a very new situation. Now the ink volumes and pigment loads can be reduced, with often 25 percent lower anilox volumes. This means less ink is used, fewer raw materials, lower cost materials, and less energy to dry, plus this can often mean higher press speeds in turn.
All of the micro surface texturizations like DigiCap NX, or its closest clone, help the densities achieved! Kodak DigiCap NX is the simplest with no loss of imager speed or increased costs. They all require flat top dot structures without oxygen inhibition to form correctly on plate, which also helps with greater impression latitude and plate life. But only Flexcel NX with pixel for pixel imaging to gives you the optimum imaging in the highlights. The others all give up the positive effect for the highlights in traditional LAMS imaging of dot sharpening through oxygen inhibition shrinking the dots to be smaller!
Image 2: Solid produced with same anilox roll and ink as Image 1 using DigiCap NX
The days of choosing highlights or solids are almost past us now as a normal practice, unless you are still using the rounded top dots of traditional LAMS plates! Yet many people still seem unaware that they don’t need to make that compromise, or accept its resultant effects in terms of costs, materials, and productivity.
Isn’t it time you proved to yourself that you don’t need or want to compromise in the same way anymore, and you really can get both at the same time? So why not try for yourself, either with Flexcel NX, alone or head to head with the competitions best? I know you will glad you did.
Dr. John’s Contact Information:
For anyone who does want to email me, please use firstname.lastname@example.org and please don’t miss out the number 3 in the address, or you will reach another John Anderson in Kodak manufacturing!
Have a wonderful day.