Solutions That Aren’t Solutions
One of the biggest problems with back doctoring is that the real cause (usually type or choice of doctor blade) isn’t addressed right when leakage first occurs. The desire to keep presses running with minimal downtime leads operators and crews to pursue the quickest solution rather than what may be the correct one. Stopgap remedies usually prove to be marginally or temporarily effective, but in many scenarios could make the problem worse:
- Increased loading pressure: Press operators frequently choose this method as a “quick and simple” solution. However, it can create more damage in the long run by placing too much pressure on blade tips, causing them to break off and contaminate ink
- Adjusting pump speed: This is another frequent solution, as it most certainly will minimize the problem, but also causes other print quality problems, like ink starvation, ghosting and anilox scoring
- Switching to thin, wider blades: Usually done on the containment side of the chamber, press crews will employ this method as a quick fix. As the press continues to run, however, this actually allows for unwanted ink debris to more easily pass under the extended, wider blade—causing a number of more severe and unwanted issues
While it may seem like these courses of action save time and money at first, by the time a printer accounts for wastage, when other print quality issues emerge, it ends up that taking the time to thoroughly investigate the issue is a smarter choice.
The Real Answer
Like all businesses, print profitability comes down to a series of choices regarding quality and cost. The best equipment in the world will fail to perform to expectations when inferior components are used. That can lose you repeat business from customers that are not satisfied with the end results. At the same time, you have to be careful with expenses related to upkeep and maintenance, because those cannot be charged to customers if you want to stay competitive in the market.
The solution lies in making smart investments that actually pay for themselves by allowing you to avoid downtime due to washing, repairs, replacement of scored rollers, and constant replacement and reinstallation of cheap, failing doctor blades. To really prevent back doctoring and the issues it causes, make sure you consider the following:
- In steel applications, specialized coated doctor blades are preferable for preventing scoring and ink contamination, and assist in preventing the back doctoring icicle problem
- Use special plastics or coated steels that are designed specifically for reducing friction and ink adhesion
- Plastic and Mylar blades of all kinds may be made to incorrect specifications. Always check your order to make sure the blade is not too thin, too thick, too short or too long
Whatever blade you choose, make certain it has a low coefficient of friction, is solvent resistant and flexible, yet stable. Even though this may result in a slightly higher cost than value priced blades, they will last longer, and exhibit fewer problems and expenses over time.
Is Your Problem Back Doctoring? Here’s How to Check
Sometimes a leak is a leak, and addressing it as a back doctoring issue may not help your situation. Fortunately, there are some fundamental warning signs that indicate if it truly is a back doctoring problem. These are a few items to review:
- Are there any telltale icicles forming on the backside of equipment?
- Does the problem persist even after adjusting pressure settings?
- Are your end seals in proper working order?
- Does the problem persist even after ensuring all chambers and anilox rolls are parallel with one another?
If you answered yes to one or more of these items, you can reduce and prevent back doctoring with the right kinds of doctor blades installed on your equipment.
About the Author: Bobby Furr is the flexo services manager at Daetwyler. He is responsible for sales and technical support of Daetwyler’s existing pressroom products and managing new products that focus on the flexo printer. He is also involved in research and development of products for the flexo and gravure industries. He has authored several technical articles, and lectures and conducts training seminars on the latest pressroom technical data. Furr has been in the flexo industry for 31 years.