A White Paper from Flexo Concepts
Gain Competitive Advantage through
Coating Quality and Press Efficiency
By Chris Nolin
Vice President of Sales
Flexo Concepts
Anilox Roll Cleaning is Essential for Consistent Coating Station Performance
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A White Paper from Flexo Concepts
Anilox Roll Cleaning is Essential
for Consistent Coating Station Performance
Gain Competitive Advantage Through Coating Quality and Press Efficiency
In these tough economic times, sheetfed offset printers are looking for ways to be more productive
and cut costs. One way to guarantee coating quality and save money is to keep the anilox
coating system in peak operating condition through regular cleaning. Like any other part of the
press, maintaining the coating system is necessary to reduce job waste, labor costs and downtime.
This paper will show how regular cleaning will keep anilox cells free
of coating residue so that they can deliver precise, consistent
volumes of coating to the sheet.
The Anilox Coating System
In sheetfed offset coating applications, the function of the anilox
coating system is to meter and control the transfer of an exact
coating film thickness from the anilox roll to the blanket cylinder and
finally to the sheet. Controlling this volume of coating is vital to
achieve uniform coverage and consistent coating results. The
anilox roll is the heart of the coating unit, and its condition has a
direct impact on a printer’s ability to deliver a uniform coating
thickness repeatedly. Variations in coating coverage can result in
expensive job rejections and press downtime.
Unlike a rubber inking roller, the anilox roll’s surface is laser-engraved
with a consistent pattern of anilox cells or tiny precision “buckets.” These
cells fill with a fixed amount of coating and then release a percentage of
this amount to the coating blanket. Each roll is engraved with a specific
cell depth and opening based on the printer’s specifications according to
his application needs.
When a newly engraved anilox roll arrives from the manufacturer, volume
is even across and around the surface of the roll. As the roll is used, however, a residual amount of
coating material is left behind in the cells after the transfer has taken place. Over time, coating
residue and dried coating deposits diminish the capacity of the cells and reduce their ability to
carry and release the volume of coating for which they were
designed. This negatively impacts coating quality, and coverage will
fail to meet the printer’s requirements.
In addition to reducing the cells’ capacity, coating residue left behind
in the cells raises the surface tension (and dyne level) of the roll. This
increases the tendency of the coating to “cling” to the surface and
prevents the roll from releasing the proper volume of coating to the
blanket cylinder. Throughout the coating system, dyne levels for each
component must be progressively higher and remain static for coating
to transfer effectively. If they increase in any component, correct volumes of coating will not be
delivered to the sheet and coat weights will suffer.
Anilox Roll Plugging
Some on-press signs of a plugged anilox roll in need of cleaning are:
Anilox Roll Cleaning is Essential for Consistent Coating Station Performance
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A White Paper from Flexo Concepts
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Inconsistent or poor coating quality
Reduced coat weights and gloss readings
Low coating consumption
Gaps in coverage and coating density
Horizontal lines running across the sheet
If build-up has occurred evenly across the surface of the roll, then the result will be less dense
coverage or a lighter coating job. In work-and-turn coating applications, light coat weights will be
inadequate to protect the sheets and jobs may be rejected. If the build-up happens unevenly, then
the result will be an inconsistent, patchy coating job. In spot coating applications, the area of the roll
that is continuously laying down coating is less likely to plug because it is continually filling with and
releasing coating. However, the negative space (areas not transferring coating) may plug and result
in gaps in coverage or “spots” in the next flood coating job where these areas of the roll will not lay
down the proper volume of coating.
If an anilox roll is left sitting in the chamber after a coating job, the area where the roll lies against the
chamber may plug with dried coating. This will appear on the sheet as horizontal lines running from
gripper to tail. (Conversely, vertical lines from gripper to tail may be a sign of anilox scoring which
requires anilox re-surfacing.) It is important to keep coating circulating or do a wash-up during the
make-ready time to prevent this from occurring.
Anilox Cleaning and Maintenance
Like maintenance procedures on other parts of the press, a maintenance routine for the anilox coating
system, where rolls are checked and cleaned on a regular basis, keeps the system running smoothly
and efficiently. Regular cleaning of anilox rolls will prevent anilox cells from plugging with
coating residue and stop build-up before it dries and becomes too difficult to remove.
Benefits of Regular Cleaning
A cleaning routine prevents fluctuations in quality that can lead to lost business. Clean anilox rolls
ensure:
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The transfer of a precise volume of coating repeatedly
Consistent coating coverage
Less downtime for reactive measures
Fewer job rejections
Reduced labor and re-working costs
Longer anilox life
It is often difficult to see when a roll is plugged, and in the absence of a maintenance routine, the
press operator must look to the finished product for signs that the roll needs cleaning. By this point,
however, finished product and coating have been wasted and the press must be shut down mid-run
for cleaning. If the roll needs to be sent out for deep cleaning or resurfacing, production may come to
a stop or charges will be incurred for rush processing and shipping. Maintaining clean rolls offers a
more predictable and convenient method of operation as cleaning can be scheduled to occur
while other parts of the press are undergoing daily maintenance.
Regular cleaning will also prolong the life of the rolls. When a rubber inking roller fails, the only option
to restore performance is to strip and resurface the roll. It is common practice in the industry to apply
this same reasoning to the anilox roll when coating quality declines. Printers are routinely sending out
rolls to be re-surfaced every 18-24 months in place of a cleaning program when, if properly cared for,
coating rolls should last 4-5 years. However, unlike a rubber roll, resurfacing an anilox roll involves
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A White Paper from Flexo Concepts
stripping, re-coating with ceramic and re-engraving the surface by laser at a cost typically exceeding
$2,000. Adherence to a regular cleaning program will vastly reduce this need and is a very real
cost saving opportunity for the printer. When a roll has become so plugged that the printer cannot
clean it and is therefore unable to achieve the specified coat weights, a good deep cleaning for as
little as $200 is often all that is needed to restore cells to their original capacity. Implementing a
cleaning routine will not only save the printer substantial re-engraving costs but also eliminate the
fluctuations in coating quality that occur as the roll condition deteriorates.
Flexo Concepts’ Three-Step Cleaning Program
Flexo Concepts’ three-step cleaning and maintenance program combines flush cleaning,
manual cleaning and deep cleaning with regular inspection to keep the system in peak
condition.
This three-step program will:
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Boost the effectiveness of the auto-wash cycle
Prevent coating build-up in anilox cells and all parts of the anilox coating system
Ensure a consistent lay-down of coating on the sheet
Minimize labor costs and press downtime for cleaning
Reduce production and coating waste
Extend the life of the anilox roll
Prevent maintenance problems
Step 1: Daily Flush Cleaning to Prevent Coating Build-up
Adding a circulation system cleaner to the auto-wash cycle is the simplest
and most economical way to ensure coating consistency without increasing
labor costs or press downtime. Flushing the anilox coating system daily with
water and a concentrated chemical cleaning solution additive keeps the coating
pigments and resins in a liquid state and flushes them out of the anilox cells
before they dry. This step maximizes the effectiveness of the auto-wash
cycle and is essential to prevent coating residue from hardening into
deposits that will require manual or deep cleaning to remove. The solution is
added to the circulation system and passed through the ink pump, chamber,
anilox roll and filter. The product can be used while the end-of-day press clean-up
is being done and removes the coating build-up from the hoses, inside of the chamber and the anilox
cells. While using ammonia as an additive is common in the industry, the high pH can be dangerous
to the roll. Choose a lower pH or buffered solution which is safer to handle and non-corrosive to metal
surfaces. Daily cleaning is particularly important if a printer is running water-based coatings because
these chemistries become very difficult to remove once they are allowed to dry. Frequently, a first
shift press operator cannot achieve the required coating strength because the rolls were not cleaned
on-press the night before and the material has set up hard in the cells. While flushing the system with
warm water may rinse some coating residue from anilox cells, using water alone does not
completely remove coating deposits and will accelerate the need for manual or deep cleaning.
As on other parts of the press, a cleaning additive is necessary for effective cleaning.
Step 2: Weekly Manual Cleaning to Remove Coating Residue
In addition to daily flush cleaning, manually scrubbing the anilox roll once or twice a week with a brush
and paste or cream chemical cleaner will loosen and remove any coating residue that may remain in
cells. (A stainless steel brush is suitable for ceramic anilox surfaces but should NEVER be used on
Anilox Roll Cleaning is Essential for Consistent Coating Station Performance
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A White Paper from Flexo Concepts
chrome-plated surfaces; brass bristle brushes are recommended for chrome.)
The cleaner is applied to the roll, rigorously scrubbed, and flushed with water.
The brush bristles are designed to create a mechanical
agitation within the cells that will remove any built-up
debris while the chemical cleaner is formulated to break
down the resins, pigments and binders so that they can
be rinsed from the cells. The roll can remain in the press
during cleaning.
Step 3: Periodic Deep Cleaning to Remove Tough Coating Deposits
While a preventative maintenance cleaning program can reduce coating residue and slow build-up,
over time a residual amount of coating material is left behind in the cells and periodic deep cleaning is
necessary to get rid of these tough deposits. Deep cleaning is done with off-press equipment that can
be purchased and brought in-house or by means of a roll-cleaning service where the roll is sent out
for cleaning. The most common methods of deep cleaning are plastic bead blasting, chemical wash,
ultrasonic and baking soda. These methods vary in cleaning effectiveness, risk of damage to the roll
engraving, water and chemical consumption, messiness and environmental impact.
The MicroClean™ Dry Media Anilox Cleaning System by Flexo Concepts is an off-press dry
plastic bead blast system which uses specially designed fine polymer beads to gently but thoroughly
remove dried coatings from anilox cells. Applied with air pressure, MicroClean media particles distort
on impact, reach the bottom of the anilox engraving, effectively sweep
away the dried coating deposits and restore cells to their original
engraved volume with each cleaning.
This is an extremely
consistent method of cleaning all the cells across and around the
roll and will result in a very even coating film thickness delivery.
A primary benefit of the MicroClean System over other methods is the
recyclability of the media. Throughout the cleaning process the
reusable media particles are separated from the spent media and
reclaimed for future use. This feature makes MicroClean the lowest
per-roll cost cleaning method currently available.
MicroClean™ Roll Cleaning Service
In addition to the equipment, Flexo Concepts offers a MicroClean Anilox
Roll Cleaning Service where printers send their rolls to the company’s
Plymouth, Massachusetts facility to be cleaned on a MicroClean
machine. After cleaning, rolls are returned to the customer within 72
hours along with a detailed report showing incoming volume and
volume gain achieved through the cleaning process.
Conclusion
For sheetfed offset printers, implementing a cleaning routine for the anilox coating system can pay off
tremendously in terms of competitive advantage, press efficiency and cost savings. The anilox
coating system, like any other part of the press, requires preventative maintenance to keep it
operating in peak condition. Regular cleaning of anilox rolls is essential to keep them free of coating
residue and ensure consistent and predictable coating results. Flexo Concepts’ three-step program
offers a simple way to maintain the system to ensure coating quality while minimizing press
disruptions, waste and anilox re-working costs.
Anilox Roll Cleaning is Essential for Consistent Coating Station Performance
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