Keeping Your Anilox Rollers Clean
Author: Frank Burgos; FlexoExchange
The ability to deliver precise, consistent, and predictable volumes of ink to a substrate has become critical as the demands and expectations of our customers have increased. Particularly in fine process printing, which involves the interplay of multiple ink color densities, accurate ink volume transfer is a must. Moreover, to compete we must be able to predict the volumes and insure that we will deliver the same volumes from run to run so that our profit margins are not consumed by color correction. Our purpose here, then, is not to address the roles of fingerprinting, separating, dot gain, factors affecting ink transfer, etc. but to discuss ways of insuring that our anilox rolls will deliver the amount of ink we expect them to, that is, how to keep our anilox rolls clean.
Hygiene: Clearly the most efficient thing we can do to keep our rolls clean is to adopt good hygiene practices. Finding what works best for your situation will likely involve the input of your press operators and press, ink, and anilox roll manufacturers. However, I'd like to offer a few general guidelines:
- Wipe your anilox rollers clean with the appropriate cleaner as soon as the roller is taken out of service. Allowing the ink to dry in the cells makes it increasingly difficult to remove. This can be especially true with water-based ink to which a cross-linking catalyst is added.
- Keep the rollers turning whenever there is ink in the system. Most presses are equipped with idling motors to accomplish this. If yours is not, it may be worth the investment for you.
- Check for and guard against the movement of air over your aniloxes. Keep them covered. Invest in a smoke gun or other means of detecting drafts (you should already have one if you use air to dry your ink!).
Chemical Cleaners: A wide variety of anilox cleaning solutions are available. These are used to keep the rollers clean between "major cleanings", such as ultrasonic cleaning or baking soda blasting (which we will discuss later). It's analogous to using toothpaste and mouthwash between cleanings at the dentist. Discuss your options with your ink supplier and your anilox roll manufacturer. Please be sure to review MSDS's and observe all applicable safety, disposal, and spill handling procedures. Two excellent cleaners that I highly recommend are HarperScientific’s CeramClean II and Strong & Safe Ani Gel by FlexoCleaners. The Strong & Safe Ani Gel is fully biodegradable and water-based.
Using brushes: I make special mention of the use of brushes because it's important not to use the wrong type of brush on your roller. Consult your anilox roll manufacturer. Often, they can supply you with the correct type for your rolls or may advise against the use of any brushes when special coatings have been applied. The following brushes are the three that I'm familiar with, but please consult your anilox roll manufacturer:
- Brass: Used to clean chrome plated anilox rolls because the soft brass won't distort the cells as might a steel brush.
- Stainless steel: Used to clean ceramic aniloxes because ceramic is harder than steel and brass brushes may actually plug the cells of a ceramic roller with brass.
- Horsehair or Nylon: Used on stainless steel anilox rollers because brass brushes may plug the cells and stainless steel brushes may wear the cells.
It's worth noting that the bristle tips of a brush are generally larger than the cells of anilox rollers used in most flexo printing. The bristles do not get into the cells. Brushing breaks the film of ink on top of the cell walls and assists cleaners through agitation.
Ultrasonic cleaning: High frequency sound waves are used in many applications where it is either difficult, impossible, or undesirable to come into direct physical contact with the offending material or where high frequency vibrations are effective in loosening the grip of a material on an object to be cleaned. It has been used for years in the cleaning of anilox rollers. The process usually involves immersing an anilox roll into a tank of water or other solvent. The roller is then bombarded with high frequency sound waves which break down the ink or other unwanted deposits, dispersing them into the solvent media. If you decide to use this method, please be sure to consult your anilox roll manufacturer and make certain that you are fully aware of any possible damage that may result in the process. If you purchase a system for in-house use, it may be wise to assign the task of cleaning to only one or a few well trained individuals. As with any chemical, be sure to consult the MSDS's and observe all applicable safety, disposal, and spill handling procedures.
Baking soda blasting: A relatively new technique used to clean anilox rollers is blasting the surface with baking soda. Fine, uniformly sized baking soda particles are air-blasted at the surface of a rotating roller. The particles are smaller than the cell openings and reach in to break down the offending material. A vacuum is used to recover the baking soda and the removed material and is collected for disposal. I've personally seen this method employed and used the roller immediately before and after cleaning with the same ink at the same viscosity, pH, etc.. It's wonderfully effective on the water based ink that I used and I feel comfortable recommending that you explore this method for your application. While the baking soda is water soluble, nontoxic, and nonhazardous, you'll need to consider the applicable disposal guidelines for the material being removed from the roller.
My purpose here has been to broadly discuss some of the options and methods of anilox roll cleaning. Therefore, I've left out many details and data regarding each of the specific methods.
If you have any questions or comments, please feel free to contact me.
Author: Frank Burgos
Web Site: http://www.flexoexchange.com/
©1997 Content of this article is original and may not be copied or reproduced without the express written consent of Frank Burgos, FlexoExchange. Except as stated previously, for one-time, non-commercial and/or educational purposes.