He continues, “For those who do have in-house ink operations, I’m shocked by how many just weigh up the batch, give it a good mix, then don’t follow through by pulling a proof and adjusting color—prior to sending the ink to press.”
Dedman acknowledges, “Time in a production facility is always a factor. Time costs money! The time factor is exacerbated by the typical practices when adjusting color on press—using what I call ‘the glug method.’ This happens when an untrained operator or assistant, who doesn’t understand color theory or ink formulation, is expected to make accurate, repeatable color adds; but instead pours in a ‘glug’ or two… or three… of whatever color he or she believes will correct the issue.”
With that on record, he immediately says, “This issue is often made worse when folks don’t understand how a spectro reading should be interpreted and color adds made based on that information. Here’s an example: let’s take a dark blue, made from Reflex Blue, Process Blue and black. The Reflex is the reddest color in that blend, while it’s still a shade of blue. The Process Blue is a blue, but compared to the Reflex, it’s a cleaner, greener shade of blue. And of course, the black is going to make the color appear dirtier and darker. Now, when comparing the color to the standard, let’s say the spectro says it needs to be less red and more green on the color sphere. I have seen folks add green to make that adjustment—when there’s absolutely no green in the formula. The correct addition would be more Process Blue to allow its greener shade to compensate for the redness of the Reflex Blue.”
Dedman observes, “Matching between colors made in different ink chemistries can be a challenge. The three main ink chemistries used in flexo printing (solvent-based, water-based and UV/LED curable) all utilize slightly different pigments, due to the limitations of each to properly disperse certain pigments.” Rendering advice on addressing the issue, he notes, “The best approach is to determine the color target well before the production run and have the color matched correctly by the ink supplier in the chemistry expected to be used for the pressrun. The same applies to matching colors previously run using other print methods—litho, digital, screen, etc.”
Beyond color match, drying and curing issues are on constant recall in this executive’s mind. “As a manufacturer of UV, LED and water-based inks for a variety of narrow web print applications, this is absolutely one of the most common issues we hear from our customers on a regular basis. In the case of drying water-based inks, the first thing we mention is the pH of the ink. If the ink’s pH is out of spec, it will begin to cause a variety of print problems, poor drying characteristics being one of them. I can’t stress this enough: If you’re having any issues on press with water-based inks, get your pH into the correct range and 90 percent of those problems will go away.”
“When you’re using the press to adjust color, you’re burning time that could be used running salable product.”
Similarly, Dedman holds, for UV-curable inks and coatings, the most common cause of poor curing is one or more of three factors:
- The age and/or condition of the UV bulb. “Most manufacturers recommend replacing every 1,000 hours of use, but I run into situations regularly when the operator can’t recall having ever replaced the bulb, or if it has been replaced, there’s no record of when and by whom. Usually when the curing unit is removed for inspection, the ends of the bulb are often blackened and many times the entire bulb surface is hazed—both conditions that will tremendously reduce the available curing power of the unit”
- Condition of the reflectors. Most folks don’t realize the energy emitted by the bulb must be reflected and focused by the reflectors in order to realize the full potential of the bulb output. Without that reflected light, the actual curing power of the unit from just the bulb surface facing the web drops to a very small percentage of total available curing power. For LED curing units, those bulb and reflector issues go away, but it’s still very important to keep the LED array clean and free of dust, ink mist, etc. to allow the full power of the LED unit to reach the ink surface
- Poor cure can be exacerbated by improper conditions for other aspects of the run. “One of the most common issues is that a UV ink won’t cure properly. A common discovery here is the anilox volume being used is way too heavy for that particular color. Zeller+Gmelin puts the bcm the color was matched to or intended to run on every label. A simple question emphasizes the point—Why is it so surprising when a dense black, meant to print on a 3.5 bcm anilox, suddenly doesn’t cure fast enough when being run at 6 bcm?”
Dedman reports that the third-most-common print issue cited by printers in his surveys involves the topic of dirty print. He expands that term to include the sub-topics of bridging, feathering, hickeys, etc. “As an ink supplier, I’m going on record to say that the majority of these print issues are typically not ink related, but can be caused by a number of factors, from poor plate making practices to dirty pressroom conditions, excessive paper dust, improper impression settings—both plate-to-substrate and anilox-to-plate—the list goes on.”
Density comes in at a prominent fourth position on Dedman’s list. “Density, again, encompasses a number of smaller sub-issues that include: low surface energy, poor ink transfer, improper anilox selection, improper anilox care and cleaning, incorrect mounting tape selection, etc.”
Dedman decrees, “All of those can be addressed, but as you might imagine, they all require very different methods and approaches, from an ink perspective.”
- Use a primer to address low surface energy
- Poor ink transfer is often a combination of ink attributes, plate surface, impression settings, etc. Ink can sometimes be modified, slightly with an additive, to help mitigate the problem
Other issues, according to Dedman, require a non-ink-related approach, His advice is, “As always, engage with your suppliers to help solve pressroom problems—they are your first and best partners, and are always willing to help.”
Poor adhesion of the ink to the substrate remains an issue that any ink supplier regularly hears about, according to Dedman. “This has always been a problem on certain challenging substrates, but it has become a more common complaint in the last few months as many printers are unable to get their regular substrates, due to raw material shortages and supply chain logistics. Hence, they are forced to substitute lower-quality materials, or must replace the normal material with a completely different option. One specific example that comes to mind was a call I received a couple of months ago from a UV flexo customer who could no longer get the regular top-coated PS material he had been running for years, but was able to get a similar PS construction, which had been print optimized for digital ink receptivity. Even though the liner, adhesive and facestock was identical, the print surface was now completely different and trying to get the UV inks to lay and adhere was a nightmare!”
Dedman concludes, “The whole conversation regarding identifying, solving and preventing print and ink issues, like these, has been happening since I started in the industry more than 44 years ago. I’m guessing they’ll continue well after I hang up my loupe and stumble into the sunset.” He issues this resounding message: “Remember a couple of key points when it comes to resolving these issues in your pressroom.”
- Follow the process. Walk through each component and action
- Ask and answer questions. What has changed? Substrate lot number, ink batch number, press settings?
- Make one change at a time. Multiple changes don’t tell you what you fixed
- Start with the least-invasive adjustment, working toward the most-invasive change—i.e., change an anilox, versus pulling the job
- Contact your suppliers! They are your most knowledgeable sources of information
You must be logged in to post a comment.