Harper Is Scientific – Anilox Technology Development

Harper Is Scientific – Anilox Technology Development

The anilox roll is widely known as the heart of the flexographic press and Harper is very proud to announce our continuing development of new anilox manufacturing technology. To someone on the outside looking in over the past few years, the anilox roll may have seemed a dormant part of the Flexographic industry. However, Harper has been very busy behind the scenes developing further advancements to take the manufacturing of anilox rolls to a whole new echelon.

The technology of manufacturing an anilox today as compared to 5 or 10 years ago is not the same. Our customers today are under more demand for consistency, repeatability and tighter tolerances. Everything is measured in the printing world from ink viscosity, dot gain, density, feeds, speeds, waste, etc. With that in mind, Harper has taken the same systematic approach in the manufacturing of anilox rolls.

Harper has made major investments and committed a massive amount of time and focus in order to scientifically measure every process of manufacturing an anilox roll.  A  major part of Harper’s investments have come in the form of new technology, equipment, software development  and instrument purchases to scientifically measure our processes in a constant effort to maintain consistency.

In our ceramic coatings process (Echoplasma) we have purchased a large number of state of the art thermal spray plasma systems. Some of these purchases are replacements as part of our continuous improvement program and others are due to increased customer demands. We will be cycling in more touch screen thermal spray units within the next year.

Additionally, as part of our ISO certification protocols we spray sample coupons from every spray booth monthly and each coupon is evaluated for hardness, density and porosity by a certified outside independent laboratory. The tracked results help us to maintain consistencies in the coatings departments at all locations. Coating consistency, besides being critical criteria, is also a top priority at Harper.  The coating of the anilox is the foundation that ensures all subsequent processes stay consistent.

The hardness of our ceramic coating averages 1200 Vickers and is operated in a range between 1100 to 1300. Some may ask why this is important and from experience, we have learned ceramic hardness above 1300 Vickers changes the mechanical property and the ceramic becomes too hard and consequently, brittle. This could cause the coating to crack under pressures normally associated during regular press operation.   By keeping the hardness of the ceramic coating within this range, we are able to provide the customer with the hardest ceramic possible to ensure longevity, while at the same time allowing it to remain very durable.

Maintaining a minimal amount of porosity is just as important as maintaining the correct hardness.  Our porosity averages ½% with an upper limit of 1%.  Keeping porosity to such a low level allows us to maintain consistency when we engrave the line screen as well as keep a uniform volume across the roll face. We also have one of the first employees in the Flexographic industry to be a certified CTSO thermal spray specialist to help maintain these standards.   For example, when engraving a 1200 line anilox with 2.0 BCM if you have porosity (coating voids) that measures 25-30 microns across it becomes impossible to hold a consistent cell shape or volume because the opening of a 1200 lpi cell is only 19 microns.  It will be impossible to create the cell wall structure necessary to prevent the low percentage dot from being overloaded with too much ink. If the opening of the cell on the anilox is greater than the plate dot you will have dirty print with inconsistent, low quality results.

Due to increased customer demand, we have added a new CNC cylindrical grinder to the grinding and superfinishing department.  As press speeds and line counts increase so has the importance of the surface finishes of our rolls prior to laser engraving.  As part of our superfinishing SOP every anilox surface is measured using a non-contact surface finish instrument and the Roughness Average (RA) is recorded. RA measuring gauges are used to measure roughness after polishing and before laser. This is very important because roughness plays a critical role in determining how a real object will interact with its environment.  All other things being equal, rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces. Roughness is often a good predictor of a mechanical component’s performance and longevity since irregularities in its surface may form cracks or corrosion. The lower the RA numbers, the lower the amount of roughness of a component.  Every anilox roll we manufacture, regardless of specification, must have a 3.0 or better RA finish before being laser engraved.  This low RA finish cannot be obtained if it was not for the less than 1% porosity of our ceramic.  To put this in perspective, we were told ceramic imaged cylinders were not possible because ceramic by nature has too much porosity.  For the past 5 years Harper’s XDI family of laser imaged ceramic gravure cylinders print without hazing because of our proprietary ceramic and finishing practices.

One way in which Harper controls consistency in the laser engraving machines is to give our operators the best possible surface to engrave. This allows our engraving machines to provide more consistent quality as well as maintain smooth cell tops. In a printer’s world this could mean a lower roughness of the anilox surface, longer blade life, and reduced scoring.

Harper globally has also extended its XLT™ technology with 9 new state of the art versatile ALE Hercules laser engraving systems, 5 of which are 500 watt models.  We also have plans to add another 4 lasers in the next 18 months. Our 500 watt fiber optic engraver contains the latest laser technology available.  As C02 laser technology became obsolete in our anilox world, the new fiber optic technology became our standard.  Low line screen engravings with extended or extreme volumes were at minimal a challenge when using CO2 technology.

However, with the 500 watt fiber optic technology we are not only able to achieve standard low line screens, but have been able to expand our engraving charts beyond what was previously possible. Harper is able to now achieve a broader range of engravings with our XLT™, XVR™, LaserKote™, Gravure Polish and XDI™ product lines. We offer more extensive engraving ranges than any other anilox manufacturer.

Harper’s laser technology goes much deeper than just the wattage of the lasers. The cell profiles are much more defined, and tops of cell walls are much more crisp and smooth. Our quality, consistency and repeatability continues to be unmatched by any other anilox manufacturer. Since Harper has pioneered and still strongly supports the 60 degree hex, we believe it is the premier engraving geometry being offered to the industry.

With that in mind, we continue to stay focused on improving upon this proven technology. Many competitors have been pursuing the quality and consistency that Harper provides with the 60 degree. But they have struggled to match it, especially in the higher line screen range. Because of such challenges our competitors have introduced different engraving patterns in an attempt to compete. However, our Harper GraphicSolutions team has run countless printing trials using every pattern and geometry available. Results of these trials along with the manufacturing innovations, the Harper 60 degree cell continues to be the most proven consistent anilox available in the market.

It is not possible to make consistent engravings if you are unable to consistently measure the line screen and volumes. Harper was the first anilox company to embrace and use Interferometry, which the FTA FQC committee has listed as the most repeatable method to measure anilox volume at the 2011 Forum. Harper exclusively uses 3DQC’s from MicroDynamics. Every anilox we engrave is set up in the laser using 3DQC measurement verification prior to engraving and then checked across the anilox surface after engraving. Harper has also developed and incorporated an internal proprietary software package to work with the 3DQC.

This gives us a quantifiable measurement of cell wall contact in the form of a percentage.This proprietary tool allows us to maintain a consistently smooth surface after engraving which will help rolls perform with less wear, scoring, and provide extended performance.

This innovation is valuable because presses are running at continually increasing speeds. Harper is proud to be the first to have this measurement capability.

Lastly, we also recognize that behind every new technological advancement or piece of equipment, stands highly skilled and dedicated employees.  It is for this reason that we constantly strive to ensure that our employees are continuously improving. Opportunities are provided for additional training on a regular basis. In fact, we give our employees the opportunity to visit a local technical college where they learn the basics of Flexographic press operation and are able to physically operate a variety of presses.

This offers valuable experience, relevance, and insight, which the employees can bring with them to apply the knowledge gained as they manufacture the world’s finest anilox rolls.

For over 40 years, Harper Corporation of America’s commitment to service and technology continues to be our global focus as the leader in anilox manufacturing, both new and remanufactured. This commitment provides our customers with the most consistent quality anilox and service – order to order; year after year.

The founders, Ron and Katherine Harper retired and sold Harper Corporation in 2006 to their highly experienced top level management team.  The new ownership team consists of the Harper’s son Jim Harper and grandson Ronald “Lee” Harper. We stay committed to continue the legacy of the Harper’s position, dedication and vision toward the Flexographic industry.

 

 

 

This commitment provides our customers with the most consistent quality anilox and service – order to order; year after year. In addition, Harper continues to be an excellent resource bringing the Flexographic industry together in forms of WalkingSeminars, Roadshows, on-site HarperGraphics Solution’s, trade shows and technical articles. This allows everyone to give and gain as much knowledge through education that the Flexographic industry has to offer.

“This commitment provides our customers with the most consistent quality anilox and service – order to order; year after year.”

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Specifying the Right Anilox Roll

 

What’s Involved?

When purchasing an anilox roll, hit-or-miss specifications can cause real problems for you down the road. Simply understanding that an anilox is made up of thousands of microscopic ink-carrying cells is not enough. It is also necessary to have a basic understanding of the characteristics of the cells and their impact on ink transfer. The following information will help you avoid unnecessary problems caused by inaccurate specifications when ordering an anilox roll.

What To Consider

There are three main cell characteristics important to understand including:

  1. The angle of the cells (60°, 45°, 30°, etc.)
  2. The carrying capacity of the cell (or cell volume)
  3. The number of cells per linear inch (or line screen)

Angle of the Cells

Other than random patterns, anilox cell angles can include the 60° hex pattern, the 30° hex pattern, and the 45° diamond pattern (as shown below).

Today, since its introduction by Harper in 1989, the 60° hex pattern is the world standard for flexo printing for these reasons:

  • The cells can be nested more tightly together, allowing for approximately 15% more cells in a given area.
  • The post areas are eliminated due to the placement of the cells during laser engraving.
  • The cells can be shallower while still releasing the same amount of ink because more cells fit into a square inch area.
  • Channeling is avoided (as compared to the 30°) because the straight side of the cell wall is not positioned horizontally.
  • This pattern is most easily reproducible from a manufacturing standpoint; therefore, you will see greater consistency from roll to roll.

45° and 30° patterns may be preferable in non-printing flexo applications (such as coatings, laminations, and specialty printing), but generally are not recommended for general flexo printing applications.

Anilox Roll Volume

The amount of ink that is transferred from a cell depends upon the carrying capacity of the cell, or the cell’s volume. Remember, you print with a wet and fluid film of ink and it is important to keep in mind that you want to print with the thinnest ink film possible. Thinner films of wet ink are easier to control, reduce dot gain, and increase graphic capability.

As shown in the following graphic, dot gain is decreased with thinner ink films, simply because there is less ink to transfer from the printing plate dot.

We are dealing with very small measurements and every micron is critical. How big is a micron?

A human hair is approximately 70 microns in diameter.

As stated before, you can use a lower volume anilox roll with a 60° cell because more cells fit into a square inch in this configuration. However, a cell with too small of a volume will cause ink to dry before it can be transferred, unless there are sufficient drying inhibitors used. The goal is to specify an anilox roll that will deliver the color strength and densities needed with the thinnest ink film possible.

As a good rule of thumb, Harper recommends a cell whose depth is between 23% to 33% of the cell’s opening.

For example, if the opening of a cell is 100 microns, the depth of that cell should be between 23 and 33 microns.

Disadvantages of deep cells (>33% depth to opening ratio):

  • Ink will not release efficiently
  • Difficult to clean
  • Creates rough cell walls
  • Extremely difficult to make consistent and predictable engravings.

Example of deep cell (50% depth to opening ratio)

Disadvantages of shallow cells (‹23% depth to opening ratio):

  • Creates rough cell cavity
  • Extremely difficult to make consistent with predictable engravings

Example of shallow cell (15% depth to opening ratio)

Advantages of bowl shaped cells (23% – 33% depth to opening ratio):

  • Uniform cell size and shape
  • Smooth glazed cell lining for efficient ink release
  • Shallow angle for easy ink release
  • Smooth, thin cell walls
  • Possible to make consistent and predictable engravings

Example of bowl-shaped cell (28% depth to opening ratio)

Remember, when using a lower volume anilox roll, less ink is transferred to the substrate. That is a good thing. However, you still need to achieve acceptable densities from your inks.

This is the point where you must evaluate the ink you’re using. If you are not getting adequate color strength, you may need to re-think your current ink choice or talk to your ink supplier to see if they have a solution. Higher pigment inks are available and ink manufacturers have responded to the demand for these inks. Though they may cost a bit more in the beginning, improved graphics more than offset the cost. Also, because you are transferring less ink, handling less ink, and wasting less ink, you will purchase less ink.

Reduced VOC emissions are another benefit of using lower volume anilox rolls. It’s the same concept: less ink gives off less VOC emissions. It’s that simple.

Line Screen

Line screen (or number of cells per linear inch) is the third major component to understand when specifying an anilox roll. Line screen is chosen in direct correlation to anilox volume.

For example, an anilox volume of 3.2 BCMs, requires a line screen of approximately 500. If an anilox volume of 3.2 BCM was engraved at 1000 line screen, cells would be much too deep. In correlation, a 3.2 BCM anilox at 120 line screen anilox would result in cells being much too shallow.

With increased ink strength and lower anilox volumes, higher line screen anilox rolls can now be used. These higher line screen rolls give printers the opportunity to reach for higher graphics with finer vignettes, line and type, and process work. Following is a rough outline of printing applications matched with appropriate line screens and cell volumes:

Application

Optimizing Research

After you understand the basic characteristics of these three, you must determine which combination of anilox cell pattern, volume and line screen will work for your application.

The best way to do this is through banded roll testing.

A banded roll contains actual bands of different line screen and volume combinations. This test helps determine the correct line screen and volume combination for printing the thinnest ink film possible and still delivering the color strength you need.

Again, knowledge of the characteristics of anilox cells and their impact on ink transfer is vital to your flexo reproduction capabilities.

In review, you need a basic understanding of:

  • The angle of the cells
  • The carrying capacity of the cell (or cell volume)
  • The number of cells per linear inch (or line screen)

By taking the time to understand these three important components of an anilox roll, you can increase your graphic capabilities and save time, money and energy in the future.

Application Appropriate Anilox Line Screen Appropriate Anilox Volume
Heavy line and solids
Line and type
Vignettes
Process		 180 – 330
200 – 400
360 – 500
500 – 1200		 8 – 4 BCMs
7.5 – 3.5 BCMs
4.7 – 2.8 BCMs
3.2 – 1.0 BCMs
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Plate Dot vs. Anilox Cell Models

The relationship of your printing plate dot to your anilox line screen cell directly affects the quality of your flexo print.

Keep in mind that when using a low line screen printing plate (such as 55) you will typically use a lower line screen anilox roll (such as 250 – 500). When using a high line screen printing plate (such as 150) you will typically use a higher line screen anilox roll (such as 600 – 1200). The following chart outlines proper anilox line count to printing plate dot relationships:

% Plate Dot
1% 2% 3% 4%
Plate Screen
(per inch)		 Minimum Anilox Line Count
(per inch)
55 500 330 280 250
65 550 400 330 280
85 700 500 400 360
100 900 600 500 440
110 900 660 550 500
120 1000 700 600 500
133 1200 800 660 600
150 1200 900 700 600
175 N/A 1000 900 700
200 N/A 1200 900 800

For example, in imperial measurements, when you are using a 100 line screen plate and trying to hold a 2% dot, the chart above indicates that you will need a 600 line screen anilox roll. Whereas, if you’re using a 100 line screen plate, and you’re trying to hold a 4% dot, you’ll only need a 440 line screen anilox roll.

The reason for this is simple. You do not want the dot on your printing plate to be smaller than the cell on your anilox roll. If that occurs, the dot can actually enter the anilox cell, picking up excess ink. This phenomena is referred to as “dot dipping” and can lead to very dirty printing situations.

The following models visually represent various line screen anilox rolls in relationship to various line screen printing plate dots. Notice that some of the printing plate dots are smaller than the anilox cells. In these situations, you will experience “dot dipping” and dirty printing. In other cases, you will notice that many anilox cells support a single printing plate dot. In extreme situations, this can lead to dot starvation and low densities on press.

Screenshot

Understanding the relationship of printing plate dots to anilox cells will help change your flexo printing process from an art to a science. By following the guidelines in this article, you should avoid the problems of dirty printing and print starvation, and save time and money in the process.

If you have further questions, please do not hesitate to e-mail technical service department, or call Harper at 800-438-3111 / 704-588-3371

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Harper Shipping Labels

Harper Shipping Labels

Click link below to download the Harper Shipping Label for:

 

Harper Corporation of America

11625 Steele Creek, Charlotte, NC 28273 USA

Resurfacing Card NC

 

Harper Corporation of America

1420 Fortune Avenue, DePere, WI 54115 USA

Resurfacing Card WI

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Harper Corporation of America Position Statement

Chemical Cleaning of Anilox Rolls

Harper Corporation of America is a customer-oriented custom manufacturer of aniloxes.  We strive to meet customer needs for many specialty applications and often that requires special corrosion protection.  We have found through the years that there is no one solution for every corrosion condition; but we have always found a solution.  At Harper Corporation of America, we work to supply our customers with aniloxes that can withstand chemical attack as long as possible.  We work from standard designs for both journal and sleeve aniloxes; but we also have numerous modifications, bonds, builds and engineering marvels that often suit the specific needs of clients.

We also have a technical support team to help customers minimize risk of chemical attack to aniloxes through training, cleaner selection, cleaning techniques and rinse procedures.  We strive to define aggravating environmental factors of exposure, dilution and temperature, and so customers can get them under control.  All we require is cooperation and a willingness to try.  When customers supply us the information, we can formulate the best possible solutions.

Certain cases may require more than one design to refine the best solution and some investment by the customer, but we will get the best combination and the most chemical resistance possible.  We are here for our customers at Harper Corporation of America. That’s what we do.

Should you have any questions or need further information, please do not hesitate to call Harper Corporation of America at (704) 588-3371 (USA & International) or (800) 438-3111 (Toll Free – Local & USA Only).

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Care & Cleaning

Cleaning methods for anilox rollers are always a hot topic in the flexo world. The following discussion outlines the most common off-press anilox cleaning systems and chemical cleaners available in today’s marketplace.

(Please Note: The following cleaning systems are not listed in any particular order.)

Baking Soda Blast (Sodium Bicarbonate) Systems:

A baking soda blast cleaning system uses air pressure to deliver baking soda media to an anilox roll. The spent media is then recovered using a vacuum unit.

Baking soda blasting works on the concept of refracture. Large sodium bicarbonate crystals break into smaller crystals upon impact. Blasting pressures reach 20-25 psi for chrome and mechanically engraved ceramic anilox, and 30-35 psi for laser engraved ceramic anilox. The baking soda actually gets inside of the anilox cells to break-up dried ink. The process seems to be effective for removing stains and dried ink.This method is capable of cleaning wide web rolls either off- or on-press, and narrow web rolls off-press only.

Off-press cleaning requires an enclosed blast cabinet, while on-press cleaning units are mobile and can be moved from press to press. Corrugated box printers typically use on-press systems to take advantage of the time saved by leaving their large rolls in the press during cleaning. In all cases, the anilox roll rotates while a nozzle mechanically travels across the roll during cleaning. Used under the manufacturer’s parameters, these units are generally safe, quick and effective for cleaning anilox rolls.Following are some suppliers of baking soda blast units:

Plastic (Poly) Bead Systems:

Plastic bead systems use air and plastic bead media to impact upon anilox surfaces at an air pressure of 35-70 psi. These systems are normally off-press units with enclosed cabinets. The anilox roll rotates while the nozzle traverses the length of the roll. The plastic or poly beads actually get inside of the anilox cells to break-up dried ink.

The process seems to be effective for removing stains and dried ink.Used under the manufacturer’s parameters, these units are generally safe, quick and effective for cleaning anilox rolls. Following are some suppliers of bead media units:

Ultrasonic Cleaning Systems:

Ultrasonic is sound energy that creates cavitation when introduced into a liquid. The cavitation is caused by pressure differentials, providing the cleaning action of this process. When using ultrasonic cleaning systems, be aware that excessive exposure time can cause cell damage.

To monitor this, ultrasonic generators are generally controlled by timers to limit exposure time and minimize damage to anilox cells. As a rule, higher line screen engravings require shorter cleaning times and are more susceptible to damage, as shown in the following examples:

Example 1: An 800-line screen roll contains 736,000 cells per square inch (wall width is 3 microns; cell depth is 8 microns.) The exposure time recommended to clean an 800-line screen roll should not exceed 3 minutes. Example

Example 2: A 200-line screen roll contains 46,000 cells per square inch (wall width is 7 microns; cell depth is 34 microns.) This lower line screen roll takes longer to clean, and can tolerate an exposure time of up to 20 minutes because wider walls are not as susceptible to damage.

The following reference table outlines exposure time recommendations for cleaning anilox rolls using ultrasonics:

Line Screen Recommended Time in Ultrasonic Cleaner
360 and below 20 minutes
380 – 440 15 minutes
460 – 660 10 minutes
680 – 800 3 minutes

Any line count above 800-line screen should be cleaned manually.

Chemical Cleaners

Chemical cleaners are used daily in the flexo printing industry and for the most part, they work. Many of these cleaners are caustic, permitting a fast and thorough cleaning. When choosing your chemical cleaner make sure you address the following items:

1. Understand EPA and OSHA issues. Make sure your cleaners are safe for use in your shop. Strict EPA and OSHA standards vary by state, and it is important to make sure your shop is in compliance.

2. Review Material Safety and Data Sheets. These documents contain valuable information about the chemical make-up of a cleaner. Be sure you understand the product and that you are taking the proper precautions when using a cleaner.

3. Consult with Your Ink Company. Before you begin using a chemical cleaner, contact your ink supplier. Some chemical cleaners may have a negative reaction with your ink, and hinder your ink’s performance.

4. Keep in Mind that Ceramics are Porous. Acidic or alkaline chemicals can migrate through ceramic and can attack the ceramic’s bond to the metal base. When ceramic is chipped, chemicals can migrate to the metal base even quicker causing the ceramic to blister and delaminate.

5. Take Care of Your Staff. The first and foremost goal is to protect the health of your employees. Normal health and safety practices require the use of safety glasses and rubber gloves when using a chemical cleaner. Understand that the pH of a chemical solution can damage your anilox roll if it is not in the safe range of approximately 4 to 11.8.

Additionally, the pH for water-based ink is typically 8.5 to 9.4, and the pH of the cleaner should always be higher than the pH of the ink to be effective. Although extremely effective at cleaning, anilox cleaners outside of the safe pH range can damage engravings with prolonged exposure. Because pH is such a vital component of anilox cleaners, having a pH meter on-hand is definitely a plus.

Generally, only anilox rolls with stainless-steel bases should be used with corrosive cleaners, because stainless steel is more corrosion-resistant than most other materials used for anilox construction. For instance, aluminum bases are much more easily corroded than steel. In fact, standard water-based inks can be harmful to aluminum-based rolls in many cases.

Brushes

A stainless steel brush should be used with chemical cleaners on ceramic anilox rolls, and a brass brush should be used for chrome rolls. These brushes will agitate the cleaner on the roll surface and into the anilox cells. A good brush has bristles with small diameters of .003 (3 thousandths) or less. At this diameter, bristles can reach the bottom of cell engravings of 280 line screen and below because the cell opening on a 280 line screen is 85 microns, or 3.34 thousandths. This does not mean brushes will not work on high line screen anilox rolls. On the contrary, brushes with chemical cleaners work well to agitate the cosmetics of the ceramic as well as the tops of the cell walls to loosen up the ink. In addition, a steel brush will not damage the anilox rolls or the cells.

Your Maintenance Routine

Achieving adequate color density and reproducing it on each successive run is the common goal of flexo printers. With the same anilox roller volume every day, you can significantly reduce color matching time. The objective is to standardize the printing process and good cleaning and maintenance routine is a part of the process. Take the time to develop a maintenance plan that works for you, and then stick with it. Taking care of your anilox rolls will save you time, money, and energy in the future.

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Anilox Volume

The amount of ink that is transferred from a cell depends upon the carrying capacity of the cell, or the cell’s volume. Volume must be accurately measured and maintained and is THE Primary Controlling Factor In Flexo Printing.

Impact on Quality Printing

 

Remember, you print with a wet and fluid film of ink and it is beneficial to print with the thinnest ink film possible. Therefore, you want to make sure your anilox volume, or cell carrying capacity, suits the specific printing needs of your operation.

Thinner films of wet ink are easier to control, reduce dot gain, and increase graphic capability. If you are trying to print with excess volumes, you will have a hard time reaching the optimum flexographic process in your facility.

Why are thinner ink films important? Because dot gain is decreased with thinner ink films, simply because there is less ink to transfer from the printing plate dot.

As shown in the photographs below, lower anilox volumes provide cleaner, sharper graphics, as opposed to the heavy print produced by the higher anilox volume below.

Thinner Ink Films Effect:

  • Dot Gain/Tonal Range
  • Contrast/Fidelity
  • Trap and Press Speed
  • Ink Mileage

Thinner Ink Films Yield:

  • Predictable Dot Gain
  • Clean Printing
  • Smaller Dots
  • Open Reverses
  • Clean Type
  • Sharp Edges

However, you still need to achieve acceptable densities from your inks.

Therefore, you must evaluate the ink you are using. If you are not getting adequate color strength, you may need to re-think your current ink choice or talk to your ink supplier to see if they have a solution. Ink manufacturers have responded to the demand for higher pigment inks. They may cost a bit more in the beginning, but improved graphics will more than offset this cost. Also, because you are transferring less ink, handling less ink, and wasting less ink, you will be buying less ink.

Reduced VOC emissions are another benefit of using lower volume anilox rolls. It is the same concept: less ink gives off less VOC emissions. It is that simple. Line screen is chosen in direct correlation to anilox volume. For example, an anilox volume of 3.2 BCMs, requires a line screen of approximately 500. If an anilox volume of 3.2 BCM was engraved at 1000 line screen, cells would be much too deep. In correlation, a 3.2 BCM anilox at 120 line screen anilox would result in cells being much too shallow.

With increased ink strength and lower anilox volumes, higher line screen anilox rolls can now be used. These higher line screen rolls give printers the opportunity to reach for higher graphics with finer vignettes, line and type, and process work. Following is a rough outline of printing applications matched with appropriate line screens and cell volumes:

Application Appropriate Anilox Line Screen Appropriate Anilox Volume
Heavy line and solids 180 – 330 9 – 4 BCMs
Line and type 200 – 400 8 – 3 BCMs
Vignettes 360 – 500 3.6 – 2.8 BCMs
Process 500 – 1200 2.8 – 0.9 BCMs

Most importantly, a printer must choose the best volume and line screen combination for their anilox roll to meet the needs of the specific job he or she is printing. One helpful tool for determining the line screen needed is a banded roll.

A banded roll contains actual bands of different line screen and volume combinations. A banded roll test helps determine the correct line screen and volume combination for printing the thinnest ink film possible and still delivering the color strength you need. Your Harper Technical Account Manager can help you run and interpret a banded roll test at your facility if you are interested.

Measuring Anilox Volumes

Anilox volumes are measured in BCMs (Billions of Cubic Microns). Keep in mind that we are dealing with very small measurements and that every micron is critical. How big is a micron? A human hair is approximately 70 microns in diameter.

At Harper, we measure our anilox rolls using Echotopography™. This measurement system uses reflected light to gather height information of microscopic surface patterns with accuracy as fine as 10 nanometers. This advanced technology allows Harper to maintain the tightest manufacturing tolerances in the industry.

With over one million dollars invested, we now bring Echotopography™ to you as our standard measurement system on every Echocel ET2000™ roll. You’ll experience the benefits in every Echocel ET2000™ roll, and at no additional cost.

The Echotopography™ measuring system provides the following benefits of other anilox measuring techniques:

  • Correlates to Press Performance
  • Standardized Volume Specifications
  • Precise Cell Volume Measurement
  • Repeatable Cell Volume Measurement
  • Non-Subjective Analysis
  • Reduced Measurement Error
  • Statistically Valid Measurement Process

Other common anilox cell measuring techniques include liquid volume measurement and microscopic measurement. Both of these techniques have inherent flaws.

Liquid Volume Measurement:

  • Does Not Address Print Quality
  • Does Not Address Cell Quality
  • Not Repeatable
  • Not Available At Set Up
  • Subjective Based On Technique

Microscope Measurement:

  • Developed for Mechanical Engravings
  • Based On Depth Measurement
  • Assumes A Particular Cell Shape
  • Wall & Opening Measurement
  • Theoretical Volume Calculation

Conclusion

Remember that anilox volume is THE Primary Controlling Factor In Flexo Printing, and it works in correlation to all other anilox properties. In addition to an understanding of anilox volume, you need a basic understanding of the line screen and cell geometry of your anilox rolls.

Knowledge of these three components will give you the ability to choose the anilox inventory best suited to your printing operation.

If you have further questions, please do not hesitate to e-mail technical service department, or call Harper at 800-438-3111 / 704-588-3371.

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Anilox Line Screen

Anilox Line Screen

By: Harper GraphicSolutions

Line screen indicates the number of cells per linear inch on an anilox roll, and is a major component when specifying an anilox roll.

Line screen is chosen in direct correlation to anilox volume. For example, an anilox volume of 3.2 BCMs, requires a line screen of approximately 500. If an anilox volume of 3.2 BCM was engraved at 1000 line screen, cells would be much too deep. In correlation, a 3.2 BCM anilox at 120 line screen anilox would result in cells being much too shallow.

With increased ink strength and lower anilox volumes, higher line screen anilox rolls can now be used. These higher line screen rolls give printers the opportunity to reach for higher graphics with finer vignettes, line and type, and process work. The following is a rough outline of printing applications matched with appropriate line screens and cell volumes:

Application Appropriate Anilox Line Screen Appropriate Anilox Volume
Heavy line and solids 180 – 330 9 – 4 BCMs
Line and type 200 – 400 8 – 3 BCMs
Vignettes 360 – 500 3.6 – 2.8 BCMs
Process 500 – 1200 2.8 – 0.9 BCMs

Impact on Graphic Quality as shown in the table above, different printing applications require different line screen counts. The reasoning behind this is that lower line screen anilox rolls typically have higher volumes and carry larger amounts of ink or thicker ink films. These thick ink films do not produce the graphic quality necessary for high-end process work. Therefore, a 330 line screen anilox roll will not be adequate when printing process flexo.

On the other hand, a high line screen anilox roll (800-1200) is not capable of laying down enough ink for a block solid job. The printer will not get enough density or coverage from such small cells. Most importantly, a printer must choose the best line screen for their anilox roll to meet the needs of the specific job he or she is printing. One helpful tool for determining the line screen needed is a banded roll.

A banded roll contains actual bands of different line screen and volume combinations. A banded roll test helps determine the correct line screen and volume combination for printing the thinnest ink film possible and still delivering the color strength you need. Your Harper Technical Account Manager can help you run and interpret a banded roll test at your facility if you are interested.

Surface Geometry Other than random patterns, anilox cell angles include the 60° hex pattern, the 30° hex pattern, and the 45° diamond pattern.

Screenshot

Today, the 60° hex pattern is recommended for most flexo printing applications for the following reasons:

  • Cells can be nested more tightly together, allowing for approximately 15% more cells in a given area.
  • Post areas are eliminated due to the placement of the cells during laser engraving.
  • Cells can be more shallow while still releasing the same amount of ink because more cells fit into a square inch area.
  • Channeling is avoided (as compared to the 30°) because the straight side of the cell wall is not positioned horizontally.
  • The 60° hex pattern is most easily reproducible from a manufacturing standpoint. Therefore, you will see greater consistency from roll to roll.

45° and 30° patterns may be preferable in non-printing flexo applications (such as coatings, laminations, and specialty printing), but ordinarily are not recommended for general flexo printing applications.

Calculating the Number of Cells per Square Inch There are two calculations for determining the number of cells per square inch of your anilox roll. One calculation is specifically for 45° cell patterns, and the other accounts for both 60° or 30° anilox configurations. Following are the calculations:

For 45° Cell Patterns:

Line Screen X Line Screen = # of Cells per Square Inch
Example: For a 500 Line Screen, 45° anilox roll:500 line screen X 500 line screen = 250,000 cells per sq. inch

For 60° and 30° Cell Patterns:

(Line Screen X Line Screen) X 1.15 = # of Cells per Square Inch
Example: For a 500 Line Screen 60° or 30° anilox roll: (500 line screen X 500 line screen) X 1.15= 287,500 cells per sq. inch

Conclusion:

In today’s flexo marketplace, it is vital that you understand the impact of your anilox line screen and cell geometry.

In addition, you need a basic understanding of the carrying capacity of the cell or cell volume. Knowledge of these three components will give you the ability to choose the anilox inventory best suited to your printing operation. If you have further questions, please do not hesitate to e-mail technical service department, or call Harper at 800-438-3111 / 704-588-3371

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Anilox Scoring Prevention

Anilox Scoring Prevention

Is scoring damage to your anilox becoming an expensive and frustrating problem? Take heart. Many printers have resolved the problem, and this article discusses how.

I. DEFINING AND IDENTIFYING SCORE LINES

When a hard particle becomes trapped between the doctor blade and the anilox roll, the particle can ride there and effectively destroy rows of anilox cells. These rows of cells appear as thin bands running the circumference of an anilox and are commonly called score lines. There are two types of anilox score lines:

  1. Deep gouging score lines which show as dark streaks in the printed image.
  2. Light polishing score lines which are more common and show as light streaks in the printed image.

Fortunately, a few easy precautions can eliminate or at least minimize the problem.

Viewing Anilox Roll Score Lines:

Figures 1 & 2: Deep Gouging Score Lines

Fig.1

Fig. 2

The two photos above show deep, gouging score lines. Notice the unharmed cells surrounding the damage. This type of score line is caused by large particles lodged between the contact tip of the doctor blade and the roll’s surface. The area damaged is always multiple cells wide and normally runs around the entire circumference of the roll.

This type of score line tends to cause a continuous dark streak in the printed graphic area.

Figure 3: Light Polishing Score Lines

The photo at left shows light polishing score lines. Notice that the cell wall is the only area damaged. The “polished looking” surface of the land area is the light score line.

These score lines reduce ink delivery volume of the anilox just enough to show as a continuous, lighter line within a graphic.

Note: A continuous, lighter line within a graphic is not necessarily caused by scoring. A plugged group of cells in need of cleaning can also print a continuous, light line. In this case, particles of metal, dried ink, or the like, actually grind into the anilox roll cells filling them in. This causes loss of ink transfer or a light streak in the printed graphic.

II. THE PRIMARY CULPRIT: BLADE TIP SLIVERS

Large pieces of metal caused by improper doctor blade use are the primary cause of anilox scoring (Figure 4).

These large steel particles break off of doctor blades as they wear.

Fig. 4

Improper Doctor Blade Use: When installing new blades, the shorter, worn blade is replaced by a new longer blade. If the chamber is not readjusted for the new, longer blade, over pressure occurs when engaged with the anilox. Press crews also over pressure to get more color to the plate without changing anilox.

Normal blade shavings do not damage a roll because the micro-slivers of metal are too small to get lodged between the blade edge and anilox cell walls.

Figure 5: Incorrect Blade Pressure

When over pressured, the doctor blade bends back causing wear on the side rather than the tip (Figure 5, shown above). As the side of the blade wears through, the tip breaks away in the form of a long metal sliver.

Ideally, only the very top of the doctor blade contacts the anilox as seen in the drawing below (Figure 6).

Figure 6: Correct Blade Pressure

When adjustment is correct, the best metering of ink, print quality and blade wear occurs. Over pressured blades from chamber alignment problems, operator error, trying to stop chamber leaking, rippled blades, or using blades for too long, create large slivers and pieces of metal which contaminate your ink system.

Viewing the Primary Culprit:

The photo below (Fig.7) shows metal, hair-like tips caused by over pressing doctor blades.

Proper blade chamber alignment (both horizontal and vertical alignment in relationship to the anilox) and maintenance of the blade chamber (cleaning, proper seal setting and blade setting) are the first and best steps toward prevention of score lines.

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Anilox Roll Cleaning Solutions

Anilox roll cleaning solutions are always a hot topic in the flexo world. The following discussion outlines the most common off-press anilox roll cleaning systems and chemical cleaners available in today’s marketplace.

(Please Note: The following cleaning systems are not listed in any particular order.)

Baking Soda Blast (Sodium Bicarbonate) Systems:

A baking soda blast cleaning system uses air pressure to deliver baking soda media to an anilox roll. The spent media is then recovered using a vacuum unit.

Baking soda blasting works on the concept of refracture. Large sodium bicarbonate crystals break into smaller crystals upon impact. Blasting pressures reach 20-25 psi for chrome and mechanically engraved ceramic anilox, and 30-35 psi for laser engraved ceramic anilox. The baking soda actually gets inside of the anilox cells to break up dried ink. The process seems to be effective for removing stains and dried ink. This method is capable of cleaning wide web rolls either off- or on-press, and narrow web rolls off-press only.

Off-press cleaning requires an enclosed blast cabinet, while on-press cleaning units are mobile and can be moved from press to press. Corrugated box printers typically use on-press systems to take advantage of the time saved by leaving their large rolls in the press during cleaning. In all cases, the anilox roll rotates while a nozzle mechanically travels across the roll during cleaning. Used under the manufacturer’s parameters, these units are generally safe, quick, and effective for cleaning anilox rolls.

Following are some suppliers of baking soda blast units:

Plastic (Poly) Bead Systems:

Plastic bead systems use air and plastic bead media to impact upon anilox surfaces at an air pressure of 35-70 psi. These systems are normally off-press units with enclosed cabinets. The anilox roll rotates while the nozzle traverses the length of the roll. The plastic or poly beads actually get inside of the anilox cells to break up dried ink.

The process seems to be effective for removing stains and dried ink. Used under the manufacturer’s parameters, these units are generally safe, quick, and effective for cleaning anilox rolls. Following are some suppliers of bead media units:

Ultrasonic Cleaning Systems:

Ultrasonic is sound energy that creates cavitation when introduced into a liquid. The cavitation is caused by pressure differentials, providing the cleaning action of this process. When using ultrasonic cleaning systems, be aware that excessive exposure time can cause cell damage.

To monitor this, ultrasonic generators are generally controlled by timers to limit exposure time and minimize damage to anilox cells. As a rule, higher line screen engravings require shorter cleaning times and are more susceptible to damage, as shown in the following examples:

Example 1: An 800-line screen roll contains 736,000 cells per square inch (wall width is 3 microns; cell depth is 8 microns.) The exposure time recommended to clean an 800-line screen roll should not exceed 3 minutes. Example

Example 2: A 200-line screen roll contains 46,000 cells per square inch (wall width is 7 microns; cell depth is 34 microns.) This lower line screen roll takes longer to clean, and can tolerate an exposure time of up to 20 minutes because wider walls are not as susceptible to damage.

The following reference table outlines exposure time recommendations for cleaning anilox rolls using ultrasonics:

Line Screen Recommended Time in Ultrasonic Cleaner
360 and below 20 minutes
380 – 440 15 minutes
460 – 660 10 minutes
680 – 800 3 minutes

Any line count above 800-line screen should be cleaned manually.

Chemical Cleaners

Chemical cleaners are anilox roll cleaning solutions that are used daily in the flexo printing industry and for the most part, they work. Many of these cleaners are caustic, permitting a fast and thorough cleaning. When choosing your chemical cleaner make sure you address the following items:

1. Understand EPA and OSHA issues. Make sure your cleaners are safe for use in your shop. Strict EPA and OSHA standards vary by state, and it is important to make sure your shop is in compliance.

2. Review Material Safety and Data Sheets. These documents contain valuable information about the chemical make-up of a cleaner. Be sure you understand the product and that you are taking the proper precautions when using a cleaner.

3. Consult with Your Ink Company. Before you begin using a chemical cleaner, contact your ink supplier. Some chemical cleaners may have a negative reaction with your ink, and hinder your ink’s performance.

4. Keep in Mind that Ceramics are Porous. Acidic or alkaline chemicals can migrate through ceramic and can attack the ceramic’s bond to the metal base. When ceramic is chipped, chemicals can migrate to the metal base even quicker causing the ceramic to blister and delaminate.

5. Take Care of Your Staff. The first and foremost goal is to protect the health of your employees. Normal health and safety practices require the use of safety glasses and rubber gloves when using a chemical cleaner. Understand that the pH of a chemical solution can damage your anilox roll if it is not in the safe range of approximately 4 to 11.8.

Additionally, the pH for water-based ink is typically 8.5 to 9.4, and the pH of the cleaner should always be higher than the pH of the ink to be effective. Although extremely effective at cleaning, anilox cleaners outside of the safe pH range can damage engravings with prolonged exposure. Because pH is such a vital component of anilox cleaners, having a pH meter on-hand is definitely a plus.

Generally, only anilox rolls with stainless-steel bases should be used with corrosive cleaners, because stainless steel is more corrosion-resistant than most other materials used for anilox construction. For instance, aluminum bases are much more easily corroded than steel. In fact, standard water-based inks can be harmful to aluminum-based rolls in many cases.

Brushes

A stainless steel brush should be used with chemical cleaners on ceramic anilox rolls, and a brass brush should be used for chrome rolls. These brushes will agitate the cleaner on the roll surface and into the anilox cells. A good brush has bristles with small diameters of .003 (3 thousandths) or less. At this diameter, bristles can reach the bottom of cell engravings of 280 line screen and below because the cell opening on a 280 line screen is 85 microns, or 3.34 thousandths. This does not mean brushes will not work on high line screen anilox rolls. On the contrary, brushes with chemical cleaners work well to agitate the cosmetics of the ceramic as well as the tops of the cell walls to loosen up the ink. In addition, a steel brush will not damage the anilox rolls or the cells.

Find the Right Anilox Roll Cleaning Solutions for Your Maintenance Routine

Achieving adequate color density and reproducing it on each successive run is the common goal of flexo printers. With the same anilox roller volume every day, you can significantly reduce color matching time. The objective is to standardize the printing process and maintain a good cleaning routine using the right anilox roll cleaning solutions. Take the time to develop a maintenance plan that works for you, and then stick with it. Taking care of your anilox rolls will save you time, money, and energy in the future.

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