How to Avoid Doctor Blade Problems and Issues

Doctor blades should never be the primary reason for a machine stop! There are absolutely no “ifs, ands or buts” about it!

Such circumstances are inexcusable. Proactive action, coupled with early intervention, should render any and every imaginable scenario, where doctor blades take exclusive blame, avoidable. It’s that simple.

Essential moves, dictated by often complimentary doctor blade analysis, will identify misaligned chambers and excessive doctor blade wear. Benefits, like extended lifetime and reduced leaking, are delivered immediately. Pressure points can be eliminated. The good news is that every action required is relatively simple to orchestrate.

TKM Stueven Clark Back doctoring
Back doctoring—ink dripping across the entire chamber into the ink pan—is a direct effect of the containment blade being positioned at the bottom of the chamber.
All images courtesy of TKM

Issues—chief among them, leaking chambers, UV ink spitting, back doctoring, premature blade wear and dot gain—while, at times challenging, can be managed and controlled. Perfect solutions, matched to individual presses, are readily available.

Here is a rundown of five major problems that result from neglect and mismanagement of doctor blade materials, selection and setting; as well as an outline of the steps to take to avoid the threats they represent—especially the potential negative impact they can have on productivity, production and profitability.

Leaking Chamber

Typically, doctor blades can be responsible for chamber leakage in the following ways:

  • Doctor blade width is not matched correctly with the end seal
  • The blade is cut to the wrong length
  • Blades are wearing out too quickly

Your blade width should always be matched to the end seal (see Image 1). Blade length should always be cut so that the ends are aligned to at least the center of the end seal (see Image 2). Leaking can also be the result of a misaligned or damaged chamber (see Image 3) or utilization of incorrect end seal material or shape (see Image 4).

Often, a leaking chamber is the result of excessive pressure used to obtain proper seal. This over-pressure then causes excessive and premature wear—not only to your doctor blades and end seals, but also to the anilox roller.

TKM Stueven Clark Image 1
Image 1: Blade width should be matched to the end seal.

The simple solution entails ensuring that the doctor blade dimensions are correct. Suppliers like TKM offer customized end seals, specific to individual press requirements. A customized seal results in lower pressure. And lower pressure prevents leaking—at the same time, it promotes increased lifetime of the doctor blade.

Whenever leaking is caused by normal doctor blade wear, various doctor blade material options can be applied to extend the lifetime and further reduce leaking.

UV Ink Spitting

UV ink has a much higher viscosity than water- or solvent-based inks. The high viscosity causes ink to hydroplane or to pass under the tip of the doctor blade, especially at higher press speeds. Never use doctor blades that were optimized for lower ink viscosities on UV-cured jobs. To prevent hydroplaning, we recommend the use of a thicker base material in conjunction with a fine tip.

TKM Stueven Clark image 2
Image 2: Blade length should be cut so the ends are aligned to at least the center of the end seal.

For example, TKM’s solution is the Stable UV doctor blade. It combines a thick base material (up to 0.012-in.) with a fine bevel tip, resulting in a clean wipe and no ink spitting, even at a faster press speeds.

Back Doctoring

Back doctoring is a common problem in wide web printing. This issue is caused by the containment blade preventing ink from returning to the chamber, and results in dripping across the entire chamber into the ink pan, particularly when the containment blade is positioned at the bottom of the chamber.

Typical causes of back doctoring and what to do about it list out as follows:

  • Too much pressure on the chamber. Lower the pressure; if not possible, then check end seals and chamber alignment
  • Wavy doctor blade. Check if the chamber and clamp are clean and free of dried ink and burrs
  • Tighten the clamps from center outward, but do not overtighten
  • Blade too thick. Use a thinner containment blade
  • Chamber misaligned. Manufacturers like TKM will analyze your used doctor blades to help confirm chamber alignment
  • Containment blade width. Follow the manufacturer’s recommendation
  • Ink viscosity. Make sure it is within specifications

Blade Wear

Once again, we must reiterate one point—doctor blades should never be the primary reason for a machine stop! Signs and risks of premature doctor blade wear include:

  • Unnecessary downtime (machine efficiency)
  • Ink contamination (metal slivers and particles; risk of scoring lines)
  • Safety concerns (extra handling of the blades)
  • Increased chamber pressure (more wear on all components—including end seals)

The first step to avoid premature doctor blade wear is to run your chamber at the lowest pressure possible.

Therefore, you must make sure that your end seals are correct and that the chamber is perfectly aligned.

TKM Stueven Clark image 3
Image 3: Leaking can be the result of a misaligned or damaged chamber.

Additionally, the correct choice of doctor blade materials and tips is very important to avoid premature doctor blade wear.

A very popular plasma-coated blade, TKM’s DuroBlade, can be used in white ink. This blade can last up to 10 million feet to 15 million feet. For expanded gamut (EG), we recommend our PowerPrint material. This blade typically lasts one week, thereby avoiding an unnecessary doctor blade change before your scheduled maintenance.

Doctor blade manufacturers offer a wide range of materials, technical support and blade analyses to overcome any premature doctor blade wear obstacles. Help is available. You can find the perfect solution for your individual presses.

Dot Gain

Dot gain means your dots increase during the printing process. This issue will increase the tone value over time, resulting in darker or fuzzy print. Many reasons can attribute to dot gain. The main reason for dot gain, as it relates to doctor blades, is the contact zone of the doctor blade is too large, or it increases during the printing process.

TKM Stueven Clark image 4
Image 4: Incorrect end seal material or shape can contribute to leakage.

Let’s look at the causes and solutions:

  • Too much pressure on the doctor blade will bend the blade. Flatten out the wear angle and increase the contact zone
  • The tip of the doctor blade is too thick. Use a thinner doctor blade (if rounded edge) or use a Lamella/preground tip
  • If you are using a plastic doctor blade, the blade usually must be thicker to prevent bending. A thinner steel blade could improve dot control. To eliminate dot gain, our recommendation is to use a steel doctor blade with a long and thick Lamella

There you have it—simple steps to make a printer’s life less stressful, more easily manageable, far more enjoyable and mishap free as well.

About the Authors

headshot Julian Stüven
Julian Stüven is the product manager/packaging for TKM Unites States Inc. He began his career in Germany in 2004 as a printer. He joined TKM Meyer near Hamburg in 2014 as a technical sales manager. Julian currently resides near Chicago and is responsible for all doctor blade sales and technical support in the US. You can reach him at [email protected].
headshot Michael Clark
Michael Clark is a technical sales manager for TKM United States Inc. He has worked for the TKM Group since 1994 and has held various sales and operational responsibilities in his 36 years in the printing industry. You can reach out to him at [email protected].