How to Choose the Right Doctor Blade for Corrugated Applications
As the marketing manager for a prominent company within the flexo industry, I field questions about doctor blades on a regular basis. By far the question that I am asked the most about blades is, “How do I choose the right blade for my corrugated application?” I’d like to take a few minutes to answer that question in terms of high quality graphic board printing and get you headed in the right direction when it comes to making your blade selection.
An absolute necessity in printing top-notch graphics is crisp doctoring performance. Proper metering will ensure that you have the correct amount of ink being laid down to create the fine images that your customers require. In general, you want a blade that ticks the following marks: long-lasting, non-abrasive, not prone to shattering (making it far less dangerous, among other obvious benefits like durability), heat and chemical resistance, and the blade must work with a wide range of inks and coatings. There are other requirements that can be added to that list, but meeting these overall standards is the best place to start and will guarantee you’ve made a wise blade choice.
There are so many blades available today that it can be overwhelming to decide which is right for you. Because of this wide selection, it’s good to know more about what you’re looking for prior to taking the leap and purchasing one. In the next few paragraphs, I’ll give you the details on the two key characteristics to think about when it comes to blade performance: shape and material.
A quick overview tells us that there are four main shapes of doctor blades, with varying uses for each. There are also five different materials that are commonly used in today’s industry, each with its benefits and drawbacks. We’ll cover the different shape options first and then get into the materials.
The four main blade shapes are stepped, beveled, square edge and rounded. Stepped blades, otherwise known as lamella blades, come in varying lengths and consist of a thick end and thin end. While the thinner end, the one that comes into contact with the roller, provides great metering, it also wears out faster than its alternatives simply because there’s less of it. Rounded blades are exactly what they sound like: round on both sides. This roundness provides an even metering throughout and can be mounted either way. Round blades are generally constant throughout the run, but their thickness is less than ideal.
The third category is a square edge blade. I strongly recommend against square edge blades for any type of doctoring because there is no smoothness about it – your best bet with one of these is to use it as a containment blade, preferably one made of plastic. And lastly in the realm of shapes: the beveled blade. A very common choice because of its immediate metering application, but it needs to be tightly monitored for wear because the ink film often increases as the contact edge grows from use.
Doctor blade materials, on the other hand, are a little more complicated of a subject than that of their shape. There are five materials commonly used to create blades today and they are as follows: plastic (UHMW/UHMWPE), stainless steel, carbon steel, tool steel and graphite. While the steel blades have upsides and are favored by many within the industry, current trends and advancements in technology are heating up the playing field for plastic and graphite.
In recent days, the most popular blade on the corrugated market has been the ultra high molecular weight polyethylene blade, or UHMWPE. A major reason for its popularity is that this particular material has a phenomenal lifespan. However, one of the biggest downsides to using this blade is that when it is used under high pressure for long periods of time, it tends to relax slightly. This relaxation means that the blade will not be doctoring as efficiently as it could be – a characteristic that is not ideal for high quality graphics. Still, there’s a reason that it’s popular: when utilized under correct conditions, it’s a great blade.
The three steel-based choices are stainless, tool and carbon. Good, high quality carbon is a great choice. Strong and reliable, it gives you the wonderful benefit of a thinner blade. If you go the carbon route, however, be sure not to skimp – inferior blades often result in debris (usually in the form of slivers) that causes scoring and print streaks. Stainless steel blades, on the other hand, are softer than carbon but a good alternative if you’re concerned about corrosive issues. The downside is that the softer material wears down faster, so a close eye on maintenance is necessary; stainless debris is no better than other steel debris, however, stainless is non-ferrous and the fragments won’t be picked up by magnets which can result in other issues. And lastly in the steel category: tool steel. An excellent choice of blade material because wearing comes in tiny particles like talcum powder, often extending the life of both blade and roll.
My personal choice for a doctor blade is one that performs like a steel blade but isn’t: graphite blades. In general terms, I recommend it for all-around performance metering, lifespan, anilox roll life and safety. The downside to graphite is that it typically doesn’t allow for the same level of metering as steel. That said, its construction provides improved spring strength and a less abrasive tendency than metal, meaning longer lifespans for your anilox rolls. Typical graphite blades aren’t notch-sensitive, making shattering very unlikely. They also have great thermal and chemical resistance properties so they’re less prone to warp or twist when heat is introduced. This last property means that they can be used with essentially any ink or coating in modern-day converting – and that’s a feat in itself.
Hopefully this has cleared up some of your questions about selecting a doctor blade and the characteristics you should look for based on your application. In the end, it’s up to you to decide what’s best for your business, but our team at Pamarco is always willing to help you with any details regarding your choice. Don’t hesitate to contact me if you have any questions or would like further information about making your next doctor blade selection.
About the Author
John Rastetter, as the vice president of sales and marketing for Pamarco’s Flexo division, is responsible for leading the Americas sales team and executing the strategies for sales in North America, Canada, Central, South and Latin America. With more than 30 years in the printing and packaging industries prior to joining Pamarco, John has held various executive positions at some of the leading suppliers to the printing industry, developing and managing sales and service organizations in North America, Asia Pacific and Europe.