With all the talk surrounding digital printing, flexography still dominates the labels and package printing space. When discussing flexo printing, the doctor blade might not be the first or second recognized component, but it is one of the most vital.

A quality doctor blade will enable label printers to control ink film thickness. The right doctor blade allows for the production of consistent, high-quality graphics, while preventing dot gain and ink spitting.

Allison Systems is continually investing in solutions that will meet demands for current and future printing requirements, including different materials, performance enhancing coatings and edge shapes.

“The best equipment, prepress, and operating procedures cannot produce quality graphics if the doctor blade fails to perform consistently throughout the entire run,” explains Bill Warner, vice president of Allison Systems. “Flexo printing requires that the doctor blade provide a constant wipe throughout the press run so that the ink volume carried by the anilox to the plate is determined only by the anilox volume.  If the doctor blade is not working correctly, the ink volume carried to the plate will include the anilox volume plus some amount of surface ink.”

Doctor blade manufacturers have had to keep up with print advancements. As technology changes in other facets of the industry, doctor blades must be adapted. Changes to inks and anilox rolls are generally more abrasive to the doctor blade, and faster press speeds contribute to blade wear. 

According to Warner, Allison Systems offers one of the largest diversities of blade materials to address the needs of the marketplace. “Our material selection includes various forms of steel, composites, and plastics so that we can provide to our customers a material that works best for their specific application and goals,” he says.

Allison Systems provides its customers with more than just blades, it offers services and packaging solutions for its materials, as well. As far as blades go, the company offers the White (CX), which is most common carbon steel blade material. It boasts high-quality steel with economical life and excellent metallurgical properties. CX has a bright, polished metallic appearance and can be used in all gravure and flexo doctoring and containment applications. Fiberglass, graphite, and mylar highlight the company’s plastic and composite products.

Steel has and continues to be the most widely used for doctor blades, with carbon steel the most popular type of steel. “Carbon steel blades are economical choices when used with short-run process jobs on non-porous substrates and inks that aren’t very abrasive,” says Warner.  “They can be used on all anilox screens along with solvent, water, and some UV inks. If corrosion is an issue, a stainless-steel blade may be a better choice but use caution when using stainless steel blades with ceramic anilox rolls as some stainless-steel materials have been associated with adhesive wear which can lead to print defects.”

Allison Systems also provides an array of composite and plastic doctor blades. Composite blades can serve as a good choice for abrasive and high solids inks. These blades are reinforced with glass fibers to help avoid the plastic deformation issues that plague un-reinforced plastic blades during a press run. However, Warner notes that a composite blade will typically allow some surface ink to remain on the anilox roll, necessitating a metal blade if surface ink cannot be tolerated. 

While these blades do not get as sharp as their steel counterparts, the composite material is harder than plastic, so the working tip is less likely to be damaged by hard particles in the ink and they are not prone to embedment problems that can lead to anilox scoring. 

Plastic doctor blades provide a lower coefficient of friction on ceramic anilox surfaces and long life. According to Warner, plastic blades have to be thicker than metal or composite blades to provide the same rigidity.  That said, the thicker material will typically leave the most surface ink on the anilox roll of all blade material types and subsequently provide less consistent print quality.

“When used as doctor blades, plastics work best for line work with less than 400 count anilox screens that are printing abrasive or high solids water based inks on paper and board substrates,” says Warner. “An area where plastic blades have been proven to be very useful for flexographic printing is on the containment side of a chambered inker. Thin, flexible polyester based blades have been successfully used as containment blades. Plastic containment blades will prevent back doctoring and particle trapping between the blade and anilox roll, as well as reduce blade related wear on the anilox. Plastic blades are the safest for an operator to handle because they are not as likely to impose a cut risk.”