What’s Your Game Plan?

Anything in excess is never a good thing. Just like overdoing it by stuffing down that last bite of pie or filling your home with unnecessary material indulgences, printers can also overdo it with an excess amount of ink. Fortunately, this is where doctoring systems come in to save the day, and the printed material. But, like any piece of printing equipment, these systems are not problem-free. That is why converters need to be armed with the knowledge and skills necessary to make sure doctoring systems run properly and efficiently.

Happy medium

A doctoring blade can only do its job of wiping away excess ink if its contact angle is just right. Improper angles can lead to inconsistent printing and damage to anilox rolls or gravure cylinders.

When setting up a gravure print job, the press operator must adjust the doctor blade to the appropriate angle (between 55–65 degrees). With too low of an angle, an excess amount of ink passes under the doctor blade, carrying unwanted ink to the substrate, says Paul Sharkey, president, FLXON Inc. Too steep of an angle removes too much ink, he says. “A lot of the newer presses have gauges on the press to set the proper angles. The only information you will need is the cylinder diameter or circumference,” says Johnny Stamey, technical product manager, Max Daetwyler. If the press does not have gauges, he suggests using an angle measuring tool to set the proper angle based on the cylinder size. Sean Teufler, technical graphics advisor, Harper Graphic Solutions, recommends checking system alignment during preventative maintenance and at least once a week to ensure the lightest pressure is used without ink or coating leakage.

With flexography, press operators should not rely heavily on the automation of newer systems. “The details and care used in setting systems have become lost in the last 20 years since the introduction of ceramic anilox rolls that are more forgiving and allow for automated chamber systems that often have extra pressure to keep ink from leaking through end seals,” says Jean Jackson, technical account manager, Allison Systems. “This extra pressure is leading to flatter doctor blade contact angles that, on the newer high speed presses or with higher viscosity materials like UV, become even lower during the pressrun.” Most modern flexo presses are automatically aligned to 30-35 degrees, and if the chamber is not over-pressured, that is where blades should remain. When the angle decreases, dot gain will be the first sign of excess pressure, says Stamey. “Sending a set of used doctor blades to the blade supplier for angle analysis will determine if [too much pressure] is the cause of the problem,” he suggests. But, Norm Davister, senior sales engineer, Printco Industries, says, “Even if the doctor blade angle is set correctly by the equipment supplier, varying degrees of printing imperfections will result with the slightest blade angle changes caused by overloading the system, [which is] usually seen when the doctor blade has been worn beyond the intended life span. The doctor blade should be replaced at this point rather than adding extra blade pressure.”

Wear and tear

In compensating for ink leakage, an over-pressured doctor blade only solves one problem by creating another. When too much pressure is placed on an anilox roll, it causes scoring on its surface. “[Cosmetic score lines appear] on the anilox roller, but disappear after cleaning. [Severe score lines appear] on the surface, but are the result of actual damage to the cell walls,” explains Stamey. Scoring can be caused by unwanted particles from new anilox rolls, unkempt systems, or hard ink that becomes lodged between the roll and the doctor blade or mixed with the ink, he says. “Normally, these items individually would not cause scoring/anilox wear, but when mixed together, these particles form minute balls of very hard matter,” Stamey explains. “When doctor blades have been pressed against the anilox roller with excess pressure, the tip or edge of the blade bends and allows hard particles to be trapped between the anilox roller and the doctor blade. These particles stay trapped until they finally work their way out from under the blade. By this time, damage, either cosmetic or severe, may have already occurred.” And that damage becomes apparent on the substrate. Hard particles can damage cell walls and create grooves in the roll’s surface, which carry extra ink and can create streaks in the print area, says Foley. He recommends using steel blades with clean, “inclusion-free” structures and small, spherical carbides. “Poorly refined doctor blade steel is often laden with unwanted amounts of phosphorous, sulfur, and excessive carbon,” he says. “While the price may be attractive, the overall cost (of replacing or re-engraving an anilox roll) is eye-opening.”

Filtering out particles before they cause damage can also go a long way. “People either don’t filter because they’re afraid the filter would restrict the flow of ink,” Sharkey says, “[or, they use filters that] do far too little.” He explains that even though an ink company may grind pigment, resin, and other solid particles to as small as 10 microns, the particles rejoin to form large clusters that become lodged behind a doctor blade. “Many think they don’t need to filter because the solids are ground so small when the ink is made. Others settle on a relative small filter vessel containing a wire basket at 40 mesh,” says Sharkey. “They often mistake 40 mesh for 40 microns when 40 mesh is actually 400 microns. [While they filter out large particles], damage is caused by particles as small as 100 microns.” He says printers that filter inks at 50 microns in 1-gallon vessels have largely eliminated print defects and damage to their blades, anilox rolls, or cylinders.

Cosmetic score lines are difficult to diagnose because of the many possible contributing factors, says Kevin McLaughlin, president of Flexo Concepts. “If it were easy, the problem would have already been addressed and resolved by the industry. Instead, it is actually a growing dilemma,” he says. In the meantime, he suggests that converters work with suppliers to ensure engravings are smooth and clean rolls upon receiving them to eliminate loose particles formed during manufacturing.

Line it up

Suppliers have found that many doctor blade holders are not up to par, causing poor cylinder or roll alignment. “Many of the blade holders in gravure are as old as the press, and they have warped and been damaged over time, [resulting in alignment problems, ink leaking, excessive pressure, or lower contact angles],” says Jackson. “If you have not had your supplier in to check your ink pumping set-up then a service call should be a first step,” says McLaughlin, who recommends frequently changing seals and blades. “While there is a cost here, most people try to get just a little too much life out of these parts and it typically costs far more than it saves.”

Successful converters are those that can strategize and think on their toes, which goes a long way in terms of dollars, time, and productivity. “[Flexo or gravure] can be compromised by insufficient attention to detail,” say Teufler. “Investing the time before a press run to make sure everything is correct makes the difference in getting successful and trouble-free press runs.” pP

Resources
Allison Systems www.allisonblades.com
Flexo Concepts www.flexoconcepts.com
FLXON Inc. www.flxon.com
Harper Corp. of America www.harperimage.com
Max Daetwyler www.daetwyler.com
Printco Ltd. www.printco-industries.com
Retroflex Inc. www.retroflex.com
Tri-X Inc. www.inkmetering.com

One Size Does Not Fit All

With so many different printing types, there is a high demand for the doctor blade supplier to provide printers with blades that work for their specific printing styles. Gravure and flexo printing processes have both changed so much during the last 10 years that the standard printing supplies cannot always address today’s demanding markets. Gravure printers are getting longer life out of their cylinders because cylinder suppliers have upgraded their equipment and processes. With longer cylinder life, printers need a doctor blade that will last longer and not damage the cylinder, which led the gravure industry to begin using more and more coated blades over the last 5 years.

Lamella or bevel tip doctor blades have been available to the gravure printer for years. Today, a printer can buy a lamella tip in almost any tip thickness he needs or wants. Tip thickness can range from 50 microns (.002˝) up to 175 microns (.007˝) and bevel blades can range from 2 to 45 degrees. These blade styles are still available as standard blades, but now are also available as coated blades.

The flexo printer only had a lamella or a radius tip to choose from. Today, with higher and higher anilox line screens, many different types of blades are being used. In the past, one blade would be sufficient to finish the job, but now it takes two or three different blade types to get the best results. It is important to inform printers that there are more blade choices than ever before and it may be time to evaluate the blade type they’ve been using. If printers want to continue to move ahead in the industry, it is up to their suppliers to help them stay one step ahead of the competition.

— Johnny Stamey, Max Daetwyler, technical product manager, pressroom products

For more doctoring systems technical tips, visit the "Ask Johnny" section of www.daetwyler.com

Shop Around

There are certain criteria that printers need to consider when purchasing a doctor blade system. A few of them include overall ease of use, installation requirements, clean-up time and price. Printers must focus on the most important function of the doctor blade system: doctoring the roll correctly and repeatedly. The other features mean nothing if the system cannot perform its primary function.

The manufacturer and purchaser must work together to be assured that both understand the operation and expectations of the doctor blade system. Both the purchaser and the system manufacturer should ask the following questions. They should be discussed, verified, and documented to help assure an uncomplicated purchase, installation, and operation.

1) What do you hope to gain by purchasing a doctor blade system?
2) What type of machine will it go on?
3) What is the maximum design speed of the machine it will be installed on?
4) Does the machine have a slow speed drive to the anilox or gravure roll?
5) What is the diameter and face length of the anilox or gravure roll?
6) Will the anilox or gravure roll be chrome or ceramic coated?
7) Does the roll have non-engraved areas for sealing?
8) What is the required print width?
9) What type of fluid will it apply?
10) What is the fluid pH?
11) What is the fluid viscosity?
12) Does the fluid require heating or cooling?
13) Is the application of the fluid compatible with the type of doctor blade system and blade material that will be used?
14) Is the correct fluid delivery system available?
15) What type of wash up system is required?
16) Do you require quick removal systems?
17) What level of automation do your require?
18) What is the distance or dwell time between the blades?
19) Size and quantity of supply and drain ports?
20) What are the material’s constructions?
21) Does the system manufacturer have references?

The above questions should be discussed in detail so that everyone has a good understanding of the end user’s application requirements as well as the capabilities of the system manufacturer. They will aid in the purchaser’s decision of which manufacturer will suit their overall needs.

— Perry Lichon, Retroflex Inc., president