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FLEXO Magazine : September 2014
It’s What’s Inside That Counts Analyzing Doctor Blade Composition & Material Makeup Paul Sharkey I n the age of HD flexo printing, choosing the right doctor blade “material” can be confusing and a challenge. Here’s why: Suppliers offer many materi- al choices, including: • Carbon steels • Stainless steels • Tool steels • Specially alloyed steels • Coated steels • Plastic Not all of these materials are equal to the task of achieving precision ink metering on an anilox roll to create the perfect ink film. Here’s a short assessment of what’s out there. But first: As you read this, keep in mind we’re talking about doctor blades and not contain- ment blades for use at the higher end of flexo, when aniloxes routinely exceed 1,000 lpi and plate screens range from 133 to 175 lpi. PLASTIC VS. STEEL The first big choice is between plastic and steel. Plastic and synthetic materials are most frequently used in non critical flexo print or coating applications, such as when printing on corrugated board and Kraft paper sacks. The composition of plastic and synthetic materials can include some combination of ultra high molecular weight polyethylene, polyolefin, polypropylene, polyvinyl chlorides, polymers, fiberglass, nylon—the list goes on. While these materials can offer long life and perform well in a variety of industrial applications, they fall short on the following critical points when used as a doctor blade to achieve precision ink film metering when compared to steel: • Inability to achieve thinnest ink film due to poor overall rigidity • Inability to achieve and maintain a consistent nick free edge during run • When reduced to a 0.006-in. or 0.008 -in. thick tip, the edge can soften and deform “All doctor blades have the potential to cut a person when being handled, including radius edged steel and plastic materials. Common sense and best practices that include the use of cut resistant gloves when handling a blade allow the majority of pressrooms to operate for years without finger and hand cuts. ” 50 FLEXO | SEPTEMBER 2014 PLANTS & PROCESSES FIFTH AND FINAL PART IN A SERIES