Best Practices: Press Cleaning

Every printer and converter knows that the best printing is tightly bound to proper press maintenance. Yet, it’s all too easy for operators to take short cuts or not pay attention to details that can make the difference between average work and that which delights customers. For flexo presses, the foremost cleaning issues revolve around anilox rollers.

Anilox rolls are remarkably complex tools, and taking care of them saves time, money and helps ensure the quality of your labels and packaging. Without proper care and cleaning, anilox rolls will not deliver the correct amount of ink. Every anilox roll supplier can tell stories about customers who insisted their anilox rolls needed replacement, only to find that the rolls had (possibly never) been properly cleaned and the cells were all but filled with dried ink.

Harper Corp., a leader in anilox roll production and restoration, notes that establishing good cleaning and maintenance routines are part of owning a flexo press. Proper roll maintenance can help ensure sufficient color density, significantly reduce the time needed for color matching, and provide consistent quality from job to job. Take the time to work with your press, ink and anilox roll vendors to develop a maintenance plan that works for your operation—then stick with it. Here are some basics:

Start and stay clean: When ink dries on a roller, it can be frustratingly difficult to remove, especially from the cells. Maintenance starts by wiping the rollers down with the appropriate cleaner for the type of ink being used as soon as a print run ends, recommends the FlexoExchange, a web resource for flexo press users. But use the right cleaner. “There are lots of cleaning chemistries out there, but there’s no magic bullet,” says Craig Shields, president and chief engineer at Graymills, a maker of a press cleaning systems. “Don’t be afraid to experiment to find the right ones.”

Then use the right brush: Given the size of the cells in anilox rolls, brushes are the obvious tool to use, but they are not all created equal. The brush’s job is to work the cleaning agent into the cells, but each type of brush has a purpose and it’s important to use the correct one for each type of roller. Always ask what your vendor recommends!

• Use stainless steel brushes for ceramic rollers because the ceramic is harder than steel. But not just any steel brush will do. The best ones will have ultra-fine bristles—a mere 3 thousandths of an inch in diameter—so they can reach to the bottom of some larger cells.
• Use brass brushes for chrome-plated rolls. Although chrome may seem like a hard surface, it actually requires a softer metal like brass for reliable cleaning. The important trait here is that brass bristles won’t damage cells the way a stainless brush could.
• Use nylon or horsehair for stainless rollers: It seems a little illogical to use nylon or horsehair on a surface like stainless steel, but using any metal brushes on stainless rollers can result in irrevocable damage.

Ultrasonics

The simplicity of ultrasonics—sound energy that creates high-frequency vibrations (called cavitation) in a cleaning solution—is attractive, but it is not a point-and-shoot option. Excessive exposure to those vibrations can actually damage cells, so most ultrasonic generators have timers to limit exposure time. According to Harper Corp., exposure ranges from 20 minutes for rollers with line screens of 360 or less and up to three minutes for screens up to 800 lpi. Line counts above 800 should always be cleaned manually.

Chemical cleaners

Virtually every flexo shop uses chemicals as cleaning agents for the simple reason that they work. However, the caustic properties that make them effective are also warning flags. Follow EPA and OSHA rules—which vary by state—for info regarding safe usage and disposal of chemicals. The Material Safety and Data Sheets that come with every container of chemical are good sources for compliance and performance information. Next, talk with your ink suppliers. Inks can react differently with some chemicals and a residue of a cleaner could affect an ink’s performance. Third, when using ceramic rollers, ask the roll supplier which chemicals are recommended. Ceramics are porous and some chemicals can penetrate the ceramic and cause degradation. And most importantly, protect your staff. Make safety glasses, rubber gloves, and even aprons, a requirement during cleaning procedures.

Finally, notes PNEAC, the Printers’ National Environmental Assistance Center, understand that different presses require different approaches. Rollers on narrow web presses can easily be removed for cleaning, while rollers on wide web presses are more often cleaned on press, a strategy that helps minimize press downtime. But neither approach should be the only one used. Determining the optimal strategy is part of that conversation converters must have with their press, ink and roller suppliers.

Cleanliness is next to top quality work. And implementing sound anilox cleaning practices will help ensure your presses deliver the best possible images. pP

To view this issue and past editions of packagePRINTING, please click here.