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Let’s Get Something Straight

What you need to know about your doctor blades

A lot more than you think goes into the manufacturing of those slender blades that silently skim excess ink off gravure and anilox rolls. In fact, knowing a little about these minor heroes of package printing can help you make educated decisions when replacing these thin strips of steel.

And, yes, it is cold steel that’s the material of choice for package printers and converters who are serious about providing the best possible print quality. But all steel is not created equal. Steel quality, be it for auto parts, razors or doctor blades, has a direct impact on performance, especially with respect to effectiveness and durability.

Steel 101

All forms of steel are alloys of iron and other elements formulated to meet the requirements of countless applications. Carbon is a key element, combining with other elements and working literally at the atomic level to provide strength and dimensional stability. You’ve probably heard the term “high carbon steel” in the description of quality steel products, such as kitchen knives. This typically means the steel has been made harder and stronger, usually through heat-treating.

Heat-treating and carbon content are key attributes in doctor blades because they help ensure hardness, durability, and how well a blade does its job. Hardness is especially critical because a blade that is too soft—or too brittle—can deform, break or crack, resulting in damage to rolls. Next, the quality and durability of the wiping edge helps minimize wear of costly rolls, ensures precise ink usage, and that you obtain print quality that keeps customers coming back. You can sanity check this right now with a call to your doctor blade or anilox roll vendor. Ask about the importance of consistent blade hardness and the advantages of durability. Then consider this: if you’re running a mid- or wide-web anilox or gravure press, your roll vendor is very likely encouraging you to use steel doctor blades rather than plastic or fiberglass alternatives, simply because there is no substitute for the hard edge of quality steel.

The straight and narrow

Under normal pressroom operating conditions, steel is very stable dimensionally and will stay within extremely tight tolerances throughout long press runs. But just as steels are not all the same, some doctor blades can vary from one end of a blade to the other—a distance of just a meter or so. And this is not depth or thickness: the blade may not be straight.

Straightness is one of the most important attributes of a doctor blade, especially for the longer blades used on mid- and wide-web flexo presses. Some blades measuring a meter or more may have as much as 10 millimeters difference (about 3/8”) between the point at which one end of a doctor blade touches a roll at the right end versus where it touches the left end of the roll. This great a difference means the blade is essentially curved. Moreover, that 10 millimeter difference leaves plenty of room for numerous problems to occur that can seriously compromise print quality and even result in additional wear on a roller. This difference can mean that labels, pouches, or other flexible packaging produced on a mid- or wide-web press can be visibly different across the press throughout a print run.

Okay, this might not matter for 500,000 one-color bags destined for the supermarket check-out counter. But it definitely matters to the brand owner at an upscale pet food company who wants 30,000 ten-pound standup pouches of dog food with 6 colors on each bag.

Straight, hard blades, that are also durable, are critically important. If nothing else, quality blades help ensure your press operators can work without worrying about having to compensate for variances in the blades being used, saving you time for labor, press-checks, and material waste, while helping ensure consistent quality.

You’re only as good as your last job

The point is that when it comes to printing, everything —everything— is important. Your customers expect top-shelf work. Brand owners select images, colors and substrates to consistently and accurately convey their identity, messaging, and brand promise on every package they sell. And they look to you, as the label or packaging converter, to ensure it happens. So be there for them.

Although consumables like doctor blades may seem trivial, choosing the right ones can make a significant difference in the labels and packaging you produce and in the trust and perception brand owners have of your business. And, cynical as it may sound, you’re only as good as your last job. In running a packaging printing business, you have enough things to worry about. Don’t let doctor blades be one of them. Better blades help ensure better results.

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