Anilox rollers spend an entire lifecycle in T&T lines leading to potential problems that impact production.
Here, Harper’s Bill Poulson gives some recommendations on how care and maintenance should always be top priority
The more that is learned in the area of care and maintenance of Anilox rollers, the less downtime and product loss will occur. Anilox rollers in the tissue industry are used in glue application and lamination processes as well as printing rollers for single colour or four-colour process towelling print lines. Other markets such as party goods and dinner napkins are also printed on tissue. What is unique about this industry is that once the Anilox is installed in press it will spend its entire lifecycle there as the tissue industry uses the same line screens and volumes. This is very different compared to other segments of the flexo industry that may have to change rollers from job to job.
Because the tissue industry’s rollers stay in the press, are very large, and the inks and glues usually do not get
cleaned out of them thoroughly, they will lose their volume capability for ink or glue transfer due to this plugging process. Cell plugging can be avoided by implementing good manufacturing practices. Once you have identified the problem you are half way to fixing it; if the problem is not identified, this can shut down the print or glue lamination lines.
Care and maintenance
Tracking wear and tear is a very important step as illustrated on the next page. This allows a tissue producer to
determine an expense budget as well as giving a snap shot of how the rollers are being handled and cared for weekly. Roller suppliers should come in periodically to perform audits and between that tissue producers should use a qualified handheld microscope to visually check for cell wall wear and ink plugging on a weekly basis.
Cleaning the anilox rolls; “Clean cells”
Daily procedures for cleaning are needed. Whether anilox rollers are used for printing ink or running adhesives, they need to be cleaned quickly and thoroughly. Again, this is where the handheld scope comes into play. Personnel should be trained on the visual inspection of an Anilox or glue roller, and don’t just depend on the auto wash systems to get this done. Remove all residual ink and this will avoid the ceramic surface from getting stained and minimise any plugging or corrosion issues. With the proper magnification it’s possible to tell if the roll is plugged, and if the bottom of the cell is visible it’s clean. If the roll is plugged with ink it will not perform as expected. Auto wash systems should be done with warm water treated with a compatible detergent that will help flush out the cells properly during the wash cycle. Use a detergent that has a safe pH level and also check the roller after the wash cycle to insure it is cleaned thoroughly.
Offline and online cleaning systems
Most T&T facilities can have an outside source come in and clean their rolls on press. One common practice is
the baking soda blast which can be attached to the press onsite without taking the roll out of the press. If the rolls plug over time and you cannot get them cleaned by hand, an online and onsite service should be scheduled for once or twice a year. It will pay itself off in product consistency and less quality control issues.
Inks and adhesives in the tissue industry can be acidic or caustic causing the ceramic surface of the roller to decay. These inks are formulated to avoid ink bleed, streaking and other such issues that can complicate ink related handling. To avoid this, make sure that the proper barrier coating is applied to the subsurface of the roller, which is the build-up material under the ceramic.
Production environment (dusty)
The tissue environment will be dusty. The print surface of the Anilox roller should be protected or covered to limit
the amount of dust that will contaminate its surface when not in use. Once the dust gets into the system it will travel through the ink train or adhesive train spreading the contamination throughout. This can promote rollers to plug cells or have issues printing acceptable product. Dust will cause print quality issues and will flow through the chamber contaminating the ink. Proper filtering needs to be in place to trap the contamination while running. If anilox roller has not been in use, clean it thoroughly before pumping ink or glue to the rollers surface.
Choosing the proper ink or glue volume
Standard Anilox volume for T&T lines is 3.5bcm to 5bcm range. This volume range may vary slightly depending
on inks, paper or other variables. If you include party napkin in this mix, the volume range will go slightly higher than 5bcm.
Glue applications: In testing for glue applications, the volume ranges will vary from what is used for printing as pictured. Most manufacturers of T&T will run periodic testing from time to time. Tissue is a very absorbent substrate so if the tissue supplier changes the tissue formula, there may be a need to retest in order to optimise ink or glue volume. When these types of changes occur, banded testing is the way to get the process optimised again.
Glue coat weight amounts are slightly more difficult to calculate than ink. This is a perfect example for running a banded roller. A banded roller is a roller that has multiple bands of line screens and volume as well as different geometries to test so that you get the optimal amount of ink or glue transfer.
“Banded roller layout”
A tissue producer may want to try a variety of geometries. Flexography typically uses 60 degree geometry which will work fine, but there are other geometric types that may work in replacement of the 60 degree. Consider speed and chemistry of inks and coatings when choosing geometry. The trihelical or 89 degree geometry on previous page works well with glue but it may allow a coating to sling at speeds above 200meters, so make sure this can accommodate any issues or side effects that certain geometries may show.
After running the banded roller, evaluate the test results and measure the final results to set the parameters needed for day to day operation. If a coating volume for glue needs to span across a variety of tissue weights, then this is the proper way to get there with accuracy. Interpret the final results and choose a volume range that will span across the full range of tissue ply and paper weights that are produced. The final volume selected needs to be at a high enough volume to allow for slight wear and still have acceptable coat weight for glue or colour strength.
Bill Poulson is the northeast technical advisor for HGS, the technical division of Anilox rollers manufacturer Harper Corp. of America.