The ink market overall is composed of numerous ink systems, all designed for particular substrates and presses. As the variety of ink systems continue to grow, so do the ink problems experienced by printers. These challenges include stability, color variation, dirty printing, excessive ink consumption, high or low viscosity, foaming, color matching, ink spitting, and inventory control.
"Probably the most prevalent problem I've run into is the amount of press-returned inks, which don't get re-used. As a result, the work-off inventory just continues to grow," says Ed Dedman, product manager, label division, Sicpa North America, Brooklyn Park, MN. This ties up a lot of money in inventory and also takes up a lot of space in a typical pressroom, and creates added confusion as to which is new ink and which is the press returned ink.
As new high speed equipment and advanced substrates continue to be introduced, a converter's ink room has slowly become an overflowing nightmare.
"The problem is that most people don't use any form of inventory control, beside the occasional physical inventory," says Darris Smith, technical service manager, Environmental Inks & Coatings, Morganton, NC. "Another problem is that they request one gallon of ink for a job that's going to take only two pounds of ink, possibly. A gallon of ink is equal to eight pounds, so automatically they have six more pounds left over. On some narrow web presses, it takes at least a half gallon just to ink up the machines, so they're always going to get that ink back," he adds.
This presents another problem. Dedman says that returned inks are often seen as undesirable. This is because, Dedman explains, "The perception is that it's harder to print with. One of the problems you encounter in a typical press room is that different press operators will make adjustments to the ink in different ways with different ingredients. Often the adjustments that are made, or the different additives that are used, are not always recorded. The biggest reason returned inks are avoided is there aren't adequate procedures and records of previous additives and adjustments."
Returned inks can be used, say the experts, provided records are kept of their use. "The solution is to eliminate the unknowns by recording on the containers what adjustments were made, how much was added, and the date that these were made. That way, the next operator who goes to use that ink can see what adjustments have been made and when. Another way, which more shops are opting for, is to use computerized software, weighing and dispensing systems that track what ink was dispensed or returned from press. When it's time for the next job, those systems will automatically prompt the operator to use the ink that's been returned to the shelf," says Dedman.
Working off the used inks keeps inventories in line. This means either getting them worked back into production or changing them into another color that is needed. "This way," says Smith, "you get rid of the used ink before it gets old. That's an ongoing issue with every printer. They have to get rid of used ink to keep their inventories in line." Naturally a certain amount of running inventory is needed just to function, but it's important to not let it get out of hand.
A real effort must be made to work off used inks. "It's good practice to have about 20 target colors — those that are big users in their print house," Smith says. "If they have any old inks that they need to be worked off, they should see if they can work them in to one of the 20 target colors."
High inventory costs from numerous ink containers, each serving a different purpose, cause many converters to wish for a simple solution, a universal ink system. But this solution is far from simple.
"We're being pressured to make more inks that do more things — 'do-all ink' — one that works on more than one substrate," says Smith. "You can do that to some extent but there is always a trade off. If you want more of one characteristic, you typically have to give up something else. You get less of one thing to get more of the characteristic you want," he adds.
According to Dedman, however, that picture is starting to change. "Increasingly, there are a number of inks available that will cross over. For water based inks as well as UV there are systems that will work very well on paper stocks, as well as carton board and tag stocks. You will see a difference when you get into the filmic substrates, because the ink really does need to be formulated differently to adhere and perform on films. So for converters who are running a lot of paper work and film work — yes, they might need to keep different ink formulations on hand.
"Of course," he adds, "this does create extra inventory, but having the proper ink for a particular job is more important, if not most important."
Ink manufacturers today are being called upon to do more for the customers that just provide ink. They're being looked upon as consultants. This is why communication is a crucial element in the relationship between ink manufacturers and converters. Pat Hague, vice president of sales, Water Ink Technologies, Lincolnton, NC, says, "A good ink supplier will be involved more in the customer's day-to-day activities to the point to where they assist in minimizing inventories. The inventory should be adequate to run the daily jobs, but not excessive."
"Narrow web customers run many different substrates. We try to have either one or two basic systems if needed. That way you have a good paper system and a film system, for non-paper substrates. We do have some customers who run one system on all of their work— and that would be the film system that they run on film and paper, but most narrow web converters run 70-80 percent paper and about 20-30 percent film. In that case they might have a paper and film system to take care of both substrates.
"I would not advise a converter to try to manipulate ink with additives," Hague cautions, "for instance, taking a paper ink, on press or in-house, and try to put additives in it to help it run on a film. If you have pressmen putting their own additives into the press, you've got down time, you've got an ink that's not properly engineered, and if you're running film without the proper inks you can have further problems down the line.
"A front-end engineered ink for particular substrates should be something that the converter and the supplier work on together. We do try to minimize the number of systems that our customers need to carry, because it eliminates their inventory, and it eliminates any expensive confusion in their pressroom."
One of the other major issues most printers face is color matching. Smith says there are several ways to get a handle on color matching. "The preferred method is correlating by using a hand proofer or draw down machine." A hand proofer is a hand-held device equipped with a rubber roller and a small version of an anilox roll. "You draw down ink with it so that you can see what the ink is going to look like before going to press. We recommend that printers get one of these devices and use it all the time, whether just for printing, or if they have an in-house print matching facility. Always check the ink before going to press," says Smith.
Color matching becomes an issue when converters mix their own colors. If a printer is doing a good amount of printing, this maybe an economical option, Smith notes. "We can furnish them with an automated dispenser and give them formulas to create matching colors for the method of printing they're using. The benefit there is that we use the same colorants but different vehicles to print on different materials. They can have one vehicle for film and another for paper, all using just one set of colorants. This way they save money because they're not paying us to mix and ship inks," says Smith. This is also a good way to control inventory, since only one colorant is kept on hand.
Stability of inks is necessary to achieve a good print job. Ink stability primarily refers to its solubility. How do press operators keep ink stable? Smith says, "Solvent and water based inks have to have some sort of amine in them for the water, and for the resins that typically are present in the inks, to stay in a fluid solution form. When the ammonia starts evaporating out, that causes problems. The ink is not soluble. The solids that are in there want to clump together, and water is evaporating out, so the viscosity is increasing, solids are lumping together, and colors get darker as they're neglected.
"What we teach is maintenance of inks or some type of pH adjuster. A pH adjuster is an amine to keep the ink fluid. You need to replace what evaporates. In this case, water and ammonia evaporate, so you have to put that back in for the ink to stay fluid. If you don't replace it, dirty print is the result."
Dedman says, "There are still inks out there that aren't stable, because of the pigment choice or the resin choice, and the ink system. They can tend to build viscosity on press, or back away from the anilox or the metering roll. If the inks become unstable, that presents a bigger printing challenge because inks need to be babied to make sure they are in the right state to print."
In order to ensure good print uniformity, and to keep the ink stable, the viscosity needs to be maintained. According to Moses Mendes, the most common way to control viscosity is by using the Zahn cup. "It's a cup with a certain size hole on the bottom which permits flow through, says Mendes, regional sales manager, process division, at Brookfield Engineering, Middleboro, MA. "It works this way: You fill up the cup, and the time it takes for the cup to empty is related to determining viscosity. The intent is to maintain a preset level of viscosity that has been given for the best job run. The evaporation of the solvent calls for continual check of ink viscosity to ensure the best run. In order to maintain proper viscosity, you need to reintroduce the solvent at about the same rate that its evaporating," he adds.
One problem with that process is that it is dependent upon the technique of the operator, which of course varies from person to person, shift to shift. Sometimes operators get so busy that they forget to do the test, and sometimes they make manual adjustments to the ink without recording what steps they take, Mendes says, which will render the control unreliable.
"Automatic control is a better option for controlling viscosity, taking the manual operation out of it," he adds. "This way, viscosity levels can be measured continuously at preset intervals. When it deviates, the ink is automatically restored to the preset value by the viscometer." The viscometer is a small device that pours small increments of additives to maintain a very smooth viscosity flow through the entire run.
Ideally, viscosity levels should be checked every half hour," says Mendes.
Maintaining viscosity is one of the most important variables needed for a good print job, because it affects color, final printability and drying. Another problem that occurs if viscosity isn't properly maintained is ink spitting.
Mike Buystedt, market development manager, Akzo Nobel Inks, Plymouth, MN, explains that "The ink actually lifts the doctor blade a minute amount and causes a little spit of ink to come through." Smith says that the result is basically an extra layer of ink on the substrate that resembles a dark spot. "We used to see it a lot with UV inks because they're quite heavy, but most of the ink companies have dropped their viscosities for UV inks, so it's not as common," he says.
Another cause of ink spitting can be the angle of the blade or the material of blade. Buystedt adds, "The ink might be a bad grind, there might be particles in the ink, there could be some contamination in the ink, or it may be that the ink wasn't ground properly and you can have small amounts of pigments that are causing it to go underneath the doctor blade. The best way to get around that is to use a backer blade, to back up your doctor blade with another blade. Or there are doctor blades that are designed for UV flexo inks that are a little bit more rigid."
Other problems are associated with the use of lower viscosity UV inks. If the substrate is porous, Buystedt says, the ink might have the tendency to dive into the material and look weak.
"To get around that you can use a higher viscosity UV flexo ink, but another challenge is that they have the tendency to create starvation. The ink actually doesn't flow very well, and all of a sudden the anilox roll may be starved for ink, even though the ink pan is full. It creates a cavitation, which causes ink starvation and results in periodic skips in the plate," he says.
Other challenges include pH balance, and balancing strength with cure. The heavier the ink the longer it takes to cure. In this case it is important to match the match the anilox roll with the ink system.
It is important to look out for pH balance, which is the acidic content of the ink, and problems occur mainly in water based inks. Mendes says that if the pH is too high, once again the ink thickens, and if it's too low then it irreversibly sets, making the ink impossible to run. That means stopping the press cleaning it up and causing unnecessary downtime. pH is maintained with a form of amine.
Buystedt says that paper ink is usually very pH stable and requires minimum maintenance. "You just add some water and small amounts of pH adjuster throughout the day. But when you run a film ink, you'll need a pH adjuster for that particular ink system and maintenance may be every 20 minutes," he adds.
"On the water based side," says Hague, "we are continuously trying to pursue the quality of the offset printing capability output on the flexographic presses."
Hague also stresses that to improve their products, suppliers have to keep up with the variety of substrates that are continually emerging, as well as communicating with converters and listening to their needs.
On the UV side, Buystedt says, "there needs to be continued work on lower viscosity, high pigmented UV flexo inks that don't have the problems that exist today."
Everyone seems to agree that the future holds a technology that will aid in the reduction of the number of inks that are necessary to meet the needs of many applications. But in the meantime, "Printers can avoid these problems by educating themselves and their operators," says Dedman. He recommends working closely with ink suppliers and taking advantage of the training and support they offer.