Doctoring Blade Selection

Several factors contribute to long doctor blade life. Coatings, proper setting of the blade, and properly selecting a blade for your application/press will go a long way toward prolonging the life of the blade, as well as other press components such as anilox rolls.

Considering the plethora of coatings and materials available to printers, blade selection today goes far beyond simply considering price. According to Perry Lichon, president of Retroflex, “While blade materials should be judged by their ability to doctor, they should also be judged for ease of handling, blade life, impact on roll wear, and overall cost.”

According to Anthony Foley, vice president of sales and marketing for Tri-X Inc., steel doctor blades continue to be the blade of choice by flexo printers seeking the cleanest and most consistent wipe throughout the entire print run.

Marty Cansler, national sales manager, pressroom products at Max Daetwyler Corp., states that the company works with gravure printers that struggle with things like hazing, streaking, and dragouts, and flexo printers that struggle with anilox scoring, blade chatter, and limited blade life. “These issues bring us special challenges to develop a new doctor blade,” he says. “In many cases, this is done through special designs of tip configurations. While this has proved to effectively address many issues, conventional doctor blade steel often reaches its limits. By developing high-wear-resistant doctor blade coatings, we have been able to achieve results that have never been achieved before.”

The right blade for the right application

One trend in the doctor blade market is selecting specialized blades for specific applications. “Printers no longer use a universal blade throughout the process, and it is not uncommon for a plant to use steel, plastic, and coated blades within the same press.” Lichon adds, “With the ever-increasing selection of doctoring blades available, we feel it is unfair to the customer for suppliers to pigeonhole a certain blade for only a particular application. The buyer needs to strive for the maximum return on investment when choosing doctor blade material.” To that end, Lichon suggests printers ask their suppliers for a variety of blade materials to test. “This will allow you to obtain firsthand knowledge of each blade material’s performance when used for your specific application and conditions,” he says.

According to Paul Sharkey, president of FLXON Inc., doctor blades have been considered a commodity and were sold and bought as such until recently. “Price was the driving concern. However, over the past few years, an increasing number of flexographic and rotogravure printers have come to realize the importance of using the right doctor blade for their applications.”

Laurie Burkel, of Printco, Inc., states that Printco constantly visits its customers to determine the most effective use for doctor blades. “As printing press manufacturers become more technologically advanced, the demand for more customized doctor blade systems grows,” she says. “Our engineers spend a lot of time thinking outside the box. As a result, our product line continues to grow.”

UV inks have continued to pose unique challenges to narrow- and mid-web flexo printers, according to Foley, with the main issue continuing to be ink spitting. “Due to its unique consistency, UV ink, when circulated in your ink stream, applies excessive hydraulic force to the doctor blade,” he says. “This often leads to unwanted ink spitting onto the printed web.” Kevin McLaughlin, president of Flexo Concepts, adds, “Some inks and coatings cannot print well using certain types of blades and today’s printing requirements call for some flexibility by the printer in selecting the correct blade for that application.”

According to McLaughlin, metal blades appear to be the predominant doctoring blade in high-screen-count, high-end graphics. Although metal blades provide high-quality doctoring in most situations, they are more difficult to handle. In many cases, they may not offer the life of a nonmetallic blade. Nonmetallic blades tend to be easier to handle and are being used primarily for coating and low-end graphics. Both nonmetallic and metal blades offer a variety of tip configurations that offer additional benefits for particular applications.

Jean Jackson, technical account manager for Allison Corp., states that Allison designs and manufactures single blade systems for flexo and gravure that minimize blade changeover times by eliminating bolts and screws, maximize blade life, and provide consistent metering through finite analysis of the system for the specific application.

Extending the life of the blade

Long-life blades come in many forms. They are typically harder than standard blades and offer various surface coatings and treatments that reduce the wear rate, providing the required onpress life to accommodate faster speeds and longer print runs. “As more and more flexo converters acquire gearless press technology, some new demands are being put on doctor blades,” says Foley. “Gearless machines are typically running at production speeds that are 50 to 150 percent faster than conventional geared presses. These elevated speeds wear doctor blades quicker and depending on the average run length of jobs, the converter may have to investigate a premium long-life doctor blade.”

Foley cautions that these blades may affect other components of the press, namely anilox rolls. “A long-life doctor blade can be a very useful tool but not if it is prone to anilox scoring, significantly reducing the effective anilox roll life expectancy.”

Proper use of the blade also provides for the maximum life of the blade. Marc Hahn, vice president of sales and marketing at AAA Press International, Inc. concurs. “Proper setting of the steel blade to the anilox roll will provide maximum life to the blade, but more importantly, to the longevity of ceramic anilox rolls themselves,” he says.

According to Jackson, the blade-life challenges of white ink led to the company creating tool-steel blades that extended blade lives by five to ten times and helped to maintain the integrity of the gravure or anilox cylinder.

Other considerations

Lichon states that the best of doctoring systems require blade material that meets the expectations of the user. To that end, do not just judge the blades, judge the supplier too. “The supplier should be judged for service, response time, and the ability to help find a blade that meets and exceeds expectations,” he says.

Keeping the entire process in mind is also important. According to Sharkey, printers have moved from price-driven doctor blade buying decisions to process improvement driven decisions. “At this level, printers are engaged in active process control and waste reduction programs focused on print quality and bottom-line improvement, he says.

Sharkey asserts that many printers are so consumed with the daily challenges of meeting today’s shipments that they are often not in a position to study their processes to determine where the greatest process improvement and waste reduction opportunities lie. “The most successful printers in terms of quality improvement and waste materialization are those who recognize the importance of forming real partnerships with key vendors who have the expertise and a proven track record in these areas,” he says. n