- July 02, 2012, Dan Foy
Choosing the correct anilox roll is critical to print quality, process efficiency, and the overall cost of printing and coating applications. With endless offerings of cell count, cell shape, and volume combinations from anilox suppliers, converters are faced with the daunting task of choosing the correct engraving specifications.
The most important engraving specification for an anilox roll and one of the primary controlling factors in flexographic printing is engraved cell volume. Volume is the capacity of the engraving in a square inch, typically expressed in units of billion cubic microns or BCM.
The anilox roll is a precision metering instrument designed to transfer a specified ink film thickness to the printing plate for desired graphic results. Higher volumes transfer thicker ink films, which provide more color for solid coverage and line work. Too much ink and finer graphic elements suffer. Lower volumes allow higher quality print by applying thinner ink films for process, vignettes, screens, and combination printing. Too little ink and density targets and Pantone color matches cannot be achieved.
A printer’s goal should always be to print with the lowest volume and thinnest ink films possible while maintaining solid ink densities for process or Pantone color matches. Thinner ink films permit higher quality print, improve process efficiency, and increase profitability.
How can anilox volume specifications alone have such an impact?
- Higher quality print—increased process printing resolution capability, less dot gain, increased print contrast, expanded tonal range, smoother vignettes, cleaner screens, less reverse fill-in, ability to print finer type, and improved solid coverage.
- Improved process efficiency—faster drying with less dryer energy required, faster run speeds, improved traps. Standardized rolls stay in press, reducing changeover times and anilox roll inventory.
- Increased profitability—sell higher quality work, produce jobs faster, less ink consumed, increased printing capacity and more business.
A very simple idea that is not discussed often enough is the fact that ink is formulated to anilox roll volume. Next time your ink supplier asks you which anilox roll you are using, you would be wise to tell your supplier the volume, not the cell count. You can say it is a 500-cell count, but with today’s laser engraving technology and volume specifications, that could mean anywhere from 3.0 BCM to 6.0 BCM. Once upon a time there may very well have been an industry standard of 3.5 BCM for a 500-cell count but not anymore.
Regardless of the original specification, what is its volume and condition now? Rolls change over time due to wear, plugging, and damage. Regular internal inspection and the monitoring of print performance, along with scheduled roll audits, provide the answers.
What if your supplier assumes that you are using a lower volume? Ink will be formulated too strong, and needless time and materials will be wasted adjusting the ink press-side.
The engraving was a 500-cell count when delivered new and will be till the day it is reworked. The volume as delivered new may have been 4.0 BCM, but it has changed due to wear. Cells are shallower, walls are wider, and volume is lower. Therefore, it does not transfer the same amount of ink and color as it did new. Should the ink supplier still formulate ink to a 4.0 BCM? Better not, or else someone will be lacking color.
“Don’t ask, don’t tell” will only get you into trouble if you speak only of anilox cell count. Clear communication is critical if ink is to be delivered “press-ready.”
If I use a lower volume, do I need a stronger ink system? The answer is likely yes.
Will it be more expensive? That answer is also yes, however, you will use less of it, and you will significantly improve your print quality and print capability.
Consider the following chart when taking into account the economics of ink and anilox selection.
|Old Anilox Volume||Decreased Anilox Volume||Anilox Volume Reduction of|
For example (substrate permitting): Currently printing with 3.0 BCM volume process anilox rolls and limited to 120 dpi process printing plates. Decrease volume by 30% to 2.1 BCM and gain the capability to print up to 150 dpi.
According to Brian Green of Liberty Printing Inks, the cost of a higher strength, water-based, process printing ink that would allow a printer to go from a 3.0 BCM volume to 2.0 BCM would be in the neighborhood of only 15%.
Kurt Hudson, director of new business development at ACTEGA Graphic Arts NAFTA, makes sure we understand that there are limits to what an ink supplier can do at respective anilox volumes. He says, “One cannot print full density reflex blue or 485 red on a 1.0 BCM anilox if printing on matte litho stock or even a semi-gloss stock. There simply needs to be enough ink volume to fill in the contours on the surface of the substrate. The smoother the stock, the less ink deposit is required to compensate for a rough substrate ‘terrain.” Given that, stronger ink systems increase price per pound by about 20%-25%.
Kurt also added a great quip from a customer of his, who, when discussing this same issue, informed him that, “I do not sell labels by the pound, so why buy ink only by the pound! I consider ink yield; how many square feet do I get per pound is the issue.” The same is true regardless of the flexographic printing market segment from corrugated to film and everything in between.
Does higher strength ink really cost more? Not if you measure and calculate the return on investment.
Worried about the cost of new anilox rolls with lower volume specifications? Printers typically have too many anilox rolls and continue to buy more. Have an anilox roll inspection conducted to see where you stand. You may already have the volumes required. Buying the correct anilox rolls for a standardized inventory will end the vicious cycle of continuous purchases for perceived printing needs.
When discussing print quality we generally jump to process printing when quality is relative throughout all graphic requirements. Solid coverage may be more significant in terms of ink consumption and quality. If the majority of your work is solid coverage and large font, decreasing volume from 8.0 BCM to 6.5 BCM reduces ink consumption by 19%. Despite conventional thinking, solid coverage may improve while increasing print capability of that print station to finer type and coarse screen work.
Printers often believe that increasing volume will improve solid coverage. This is true to a point of saturation where solid ink density or color actually decreases when too much ink is applied. Thinner ink films applied with proper volume, cell geometry, and cell counts minimize or eliminate issues of mottling and pinholes in solid coverage.
If we focus on white, metallic, and fluorescent inks the quality and economics could be even more significant, due to the higher cost of these inks, as well as access to new markets.
Ink is not the only material transferred by the anilox roll. Coatings and varnishes add to the cost of jobs and could make or break an order with added cost of excessive materials and sacrificed coating quality.
Even for the smallest printer, a double-digit decrease in ink consumption along with the added benefits to print quality, process efficiency, and profitability is critical in today’s competitive marketplace. Many printers could run the job, but can they do it as efficiently as you?
How then do you determine the lowest volumes you can run?
The best answer is to charge your anilox and ink suppliers with collaborating to determine what that volume is. Done properly, a single phone conversation can provide the lowest volume a printer can use for the printing required. Suppliers have intimate product knowledge and practical industry experience. Take advantage of it or struggle through the learning process yourself.
Once volume is determined, a single anilox roll is engraved to the specified volume, installed and tested with a plate that contains appropriate graphic elements to be printed at the respective volume. Plate may include tonal scales for process work, vignettes, screens, type, line work, and solid coverage. This is referred to as benchmark testing and provides proof of expected print results. Based on printed, measured results, subsequent rolls are engraved at the same or adjusted volumes.
Benchmark testing can be focused on volumes for process printing, vignettes, screens, line, type, solid coverage, or any combinations thereof.
If multiple rolls are required, place the order for all rolls, take delivery of one engraved as the benchmark, run the test, and based on the performance of the first roll, specify the balance. Therefore, time and potential failures are averted. Why take delivery of rolls that might work?
Understanding that one volume specification will not cover all printing requirements, every effort should be made to standardize your inventory with as few volumes as possible. Volumes should be identified for process, combination, and line work/solid coverage.
BANDED ROLL TESTING
For a more scientific approach, banded roll testing utilizes a single anilox roll engraved at various volumes and/or cell shapes. When designed properly, the highest volume transfers too much ink, while the lowest volume provides too little. Some place between lies the exact volumes for process, combinations, vignettes, screens, line work, and solid coverage. Banded rolls can be designed for all ink applications or focused on a particular segment such as process and combination work.
The printing plate, for the banded roll test, consists of the same graphic elements utilized for the benchmark roll and are repeated on every band. Influence of volume/ink film thickness, cell shapes, and cell counts are measured and inspected across the width of the sample. Solid ink densities and color match are still the targets for the lowest volumes possible.
Minimizing or eliminating this important element of the flexo process will pay off with significant reduction in ink consumption, print quality, process efficiency, and profitability.
Ink and anilox roll work together with other elements of the process to determine success or failure. Changing engraving specifications of the anilox roll(s) invariably requires adjustment to the existing ink system. Significant changes in anilox volume may dictate a completely new ink system. Communication between key suppliers will ensure that the correct specifications and products are offered to achieve desired goals. Practical testing will guarantee the results.
What route will you take on the journey of print quality and process efficiency? Are you a tourist seeing and doing what’s already been done? Or are you an explorer taking the road less traveled to discover new and improved methods for increased profitability. The choice is yours. I suggest you get a map and take the scenic route.
Dan Foy is technical service engineer for ARC International, based out of Charlotte, NC, and can be reached at 704-562-8587. With almost 20 years of experience in the anilox roll industry, he offers proactive recommendations on anilox roll specifications, testing, inventory management, coating applications, and training, drawing from experience in production, technical service, parts and supplies, and technical sales.
His experience covers the spectrum of flexographic markets including: wide web film, foil, folding carton, corrugated, newspaper, towel, and coating applications, as well as narrow web tag and label, envelope, pharmaceutical packaging, and coatings.
He has shared his experience with students, faculty, printers, co-suppliers, OEMs, and print buyers through technical presentations at national and regional industry forums, sales meetings, and in-plant seminars. With many technical articles published in industry trade publications, his message has reached printers throughout the US and abroad.