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Ink Troubleshooting



Education and teamwork between printers and ink makers can be the key to solving specific ink challenges.



By Jack Kenny



Published April 11, 2011
Related Searches: UV curing Label industry Flexography
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Photos courtesy of Color
Resolutions International
Ink is one of several variables in the printing process. Like substrates, printing plates, printing impression, anilox roll metering and web tension, ink will help determine whether the finished product is good or otherwise. In flexography, the dominant print process for the narrow web label industry, inks have been improved along with the other variables to promote consistency and eliminate unwanted variations in print quality. Flexo today is far from what it was two decades ago, when getting a color right was an art. Now the results are increasingly measurable, so that a Coca-Cola red doesn't shift to become something that the customer does not want.

Press operators and production supervisors are no strangers to the challenges that can arise with a difficult print job. Experience tells them where to look to find and solve a problem. But occasions arise when solutions are not readily apparent. Is it the ink? Is it the UV curing system? Today's inks tend to be more stable than those of the past, but variations can be encountered from one supplier to another.

"One of the main difficulties that we see among printers today is achieving color consistency from batch to batch," says John Signet, director of marketing for ACTEGA WIT, the former Water Ink Technologies, Lincolnton, NC, USA. "When you put the ink into the press and run a job for a certain product SKU, and it doesn't match with the next batch, you're looking at variability in formulations and strength levels between suppliers. And then, when taking the ink from the ink room to the press, how quickly do you get up to the correct color?

"This relates to productivity and efficiency," he says. "You have to have an ink match that is consistent in color from batch to batch, and the anilox set up to deliver proper ink film thickness. That's where we have succeeded over the years, producing a consistent product, batch to batch."

"One thing I see with narrow web versus paper packaging and others, is that narrow web printers are more resourceful about solving problems than are the printers in other niches," says George Sickinger, president of Color Resolutions International, Fairfield, OH, USA. "The challenges are always a new substrate, the adhesive on it, the different designs. The day-to-day things, such as color matching, they pretty much do on their own."

"Knowing how to make ink or match colors is not really enough today," Sickinger adds. "The ink maker has to understand the printer's whole process, from prepress through finishing. Whether it's UV curable or water based, or a shrink application, we have to understand that whole process."

Joe Krstulic, senior national liquid product manager for INX International, Schaumburg, IL, USA, says he finds that converters tend to have issues with inks as they relate to press speeds. "The biggest problem is trying to get the proper speeds," he says. "Most narrow web jobs are printed on different substrates: papers, foils, films. In most cases you need more than one ink system to be able to get the results you are looking for. If you try to utilize one ink system for different substrates, you will have speed problems. Film inks, for example, need to dry much faster than inks on paper, and therefore need to be tended to much more. It's critical to check the viscosity and pH on a regular basis.

"To come up with one ink system that covers all of these different substrates would be a great thing," Krstulic says.

Maintaining pH
"Operaters don't always understand inks. Many of them are not properly trained on how to use ink properly. A lot of times they think they know how to handle ink properly, but the results prove otherwise." This is the opinion of Mike Buystedt, director of sales for Flint Group Packaging Narrow Web, Plymouth, MN, USA. Buystedt says that when working with water based flexo inks, the pH level is critical, and failure to maintain it will cause problems on press.

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. The term refers to the concentration of dissolved hydronium ions (H3O+). The pH of pure water is neutral at 7.0 at 25 °C (77 °F). Solutions with a pH below 7 are said to be acidic, and those with a pH higher than 7 are basic or alkaline. A low pH indicates a high concentration of hydronium ions, while a high pH indicates a low concentration.

In the past, says Buystedt, water based inks had to be adjusted roughly every half hour through the addition of amines (derivatives of ammonia) in a solution to correct the pH, which would wander out of adjustment because of evaporation. "pH is so important," he says. "With newer inks you have to correct the pH probably once a day, maybe even longer than that. Amines are added to the ink to assure that you maintain a good pH throughout a run."

Typically, he adds, the desirable pH range for water based inks is 8.5 to 9.5. "Specialty inks, such as metallics, are lower," Buystedt says.

"There has to be a balance of keeping the ink 'open' or 'wet' at the print station, but still be capable of drying before the next print station is reached," says Kirk Franklin, vice president of technology narrow web for Environmental Inks, a member of the Siegwerk Group. "Proper pH maintenance is crucial. The composition of the maintenance solution and the quantities used have to be carefully selected for the ink system and the press capabilities."

The development of pH stable inks over the years has eliminated the need for constant testing at press side. These inks, according to Buystedt, have slower amines. "Inks used for printing on paper can get away with faster amines, which will dry faster, and have more water resistance," he says.

"All you really need to do with water based inks is monitor the additives," he notes. "Alcohol speeds up the drying, glycol slows down the drying. But those are for use in special situations, and should not be used at press side."

"The stability of the pH in the ink depends on several factors: the atmosphere in the pressroom, the time of year, the drying speeds, water resistance," says George Sickinger. "These determine whether the amines stay in for a long time or forever."

"Most water based formulations today are press stable," says John Signet. "We had those systems years ago, but the days when the press operator needed to be a chemist have passed.

"We have customers with long runs who are continuously adding fresh ink. If you are not refreshing the pan you will have to do something to make the ink stable, but it's not like it was 20 years ago."

Joe Krstulic says that the pH of an ink should be checked on an hourly basis. "What you have, basically, is an acid resin that is not soluble in water. You have to modify the water with amines. In most cases, a typical ink will have 2 to 4 percent amines. As these evaporate, the pH of the ink will drop. And as the pH drops, the viscosity increases. With the drop in pH, you find that the ink doesn't print that clean, so the resin loses its solubility," Krstulic says.

Many ink companies have produced what they call pH neutral inks, which have a pH that ranges from 7.0 to 7.5. Krstulic and others say that these ink systems are expensive, and "that's why they never took off."

ACTEGA WIT makes a pH neutral ink that is used by some customers. "What we do is replace the resins in the system with others that are pH neutral, which gives a stability over the more traditional ink formulations," Signet notes. "But what you sacrifice is printability and other performances. If you are printing on paper or other absorbent substrates, a pH neutral ink can work well there, but in narrow web more than likely not."

UV inks
Water based inks are still king in the flexo world, but inks that are cured under ultraviolet light continue to gain in popularity among narrow web converters. "UV ink is a no maintenance ink," says Buystedt. "If you have a UV ink that's working right from the get-go, it just runs. You don't have to worry about maintenance." Technically a solid and not a liquid, UV curable ink does not have pH issues because it contains no water and therefore will not evaporate.

Still, the press operator must have an understanding of the entire UV system in order for the inks to cure properly. "You have to have the right bulb along with the right ink thickness," Buystedt adds. "If you're putting down ink too heavily, particularly a dark color with a high volume, it won't cure properly." Black and white inks, he says, are the two most challenging colors to cure at high volumes; black pigment absorbs UV light, so the light cannot excite the photoinitiators that trigger the curing process; and white ink reflects UV light. "The solution is to either increase the lamp power or decrease the ink coat weight. We can make a special formulation and add photoinitiators, but we have to know the printer's situation."

UV curable inks can present three common challenges to the printer, says Kirk Franklin. These three are spitting or blow-by, dive-in, and cure. "Spitting can be controlled by lowering the viscosity of the ink, if possible," he says, "and by using a doctor blade with the right composition. Dive-in can be addressed by adjusting the speed of the press and the curing lamp wattage. The overall cure involves the correct lamp wattage, lamp maintenance, and press speed."

Often a printer will call an ink supplier with a complaint that the ink is not curing properly, but the ink manufacturers say that the problems mostly have to do with the UV lamps and how they are being used.
"Typically, what does go wrong is that the printer doesn't keep the lamp wattage up to the right level, and doesn't keep the lamps clean," says Sickinger. "The inks are a lot more user friendly than they ever have been."

Signet agrees. He says, "We tend to find that the condition of the lamp systems are the problem. We encounter dirty or worn bulbs, dirty reflectors, and shutters not opening."

Krstulic offers this advice: "Make sure that the lamps and bulbs are checked on a regular basis for cleanliness and for power output. The lights themselves will lose power over time, and dirt is a big problem.

Education
Not all printers take advantage of the knowledge of ink manufacturers when they encounter a challenge, but those who do know that the vendor can be a source of knowledge. "The printer has to get with the supplier to make sure that the ink is right coming in the door," John Signet says. "We are able to show how to dial in the ink room proofing system so that it will match on press. It might have been taking them 20 minutes to get up to color, but we can usually get it where it should be in five minutes.

Ink manufacturers are more than willing to visit converters to offer education in ink handling and troubleshooting. "We will go in and put on individual ink seminars with our customers," says Joe Krstulic of INX International. "We cover everything, including ink components, the importance of pH, viscosity, ink handling, what to check for, balance, and a lot more."

At Color Resolutions International, the team prepares for their education of converters by meeting with fellow suppliers to discuss industry trends. "We started this about four or five years ago," says George Sickinger. "Every 18 months or so we bring in co-suppliers and have a summit meeting. Each party talks about what's new in their niche. The purpose is to learn what is new and to support each other. We have the substrate people, the press manufacturers, the anilox roll makers, and so forth. We're thinking about inviting one or two customers as advisers, to find out what they think and get their input."

Ink management
One way to streamline ink handling in a printing plant is to incorporate an ink management system. Producing special colors can be accomplished by ordering custom blends from the ink supplier, or they can be created in-house. Such systems allow printers to re-use small batches of inks that were left over from an earlier job, rather than dispose of them.

Ink management systems have been around for years, though not everyone in the narrow web converting industry has them. "They're not common in the label industry," says Buystedt. "Some of the larger companies make inks from dispersions and blend vehicles from their ink suppliers. That would require an ink technician full time."

The systems are generally composed of a scale, a computer with special software, and a blending unit. They permit the creation of custom colors in the precise quantities needed for a job; they reduce ink waste; and they improve productivity because they get the inks to the press quickly. They also can allow for ink inventory management.

"We have a small scale system that allows them to mix what they need – small amounts – and take care of a quick order turnaround," says Signet. "With the system you have PMS colors as well as brand colors."

"Ink mixing is similar to what happens at a Lowe's or Home Depot paint center," says Franklin. "It's basically a matter of blending measured quantities of liquids. The printer's ink technician needs to understand color and color matching, as well as how his proofing methods correlate with the presses, or more specifically the aniloxes used on the presses. Viscosity control and pH levels are critical at the prepress level. The number of narrow web printers mixing their own colors is not known, but seems to be increasing."


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