Anilox Rolls Are Key When Printing Corrugated Board

Published: August 01, 2000, By Claudia Hine, Senior Editor

Printing on corrugated board is like printing on air," says Fernando Jorge da Silva, production manager at AssiDoman Packaging Benelux B.V. in Eindhoven, the Netherlands. "Corrugated board does not have a solid underground to print on, so we need to have tight control over all aspects of the production process to be able to manufacture a high quality product."

Da Silva should know. In the Eindhoven plant, 143 employees produce and print corrugated board 24 hours a day in three shifts five days a week.

AssiDoman AB is headquartered in Stockholm, Sweden, with saw mills, pulp and paper mills, and production plants in 18 countries. The group is divided into five business units. The packaging business unit has nearly 80 production plants and sales offices in 14 European countries.

There are two departments in Eindhoven. One department converts paper rolls into sheets of corrugated board using machines from Peters (and another supplier no longer in business) to manufacture the liner and fluting. These machines are equipped with rolls from Apex for the application of glue, both single- and double-face. The sheets vary in width (from 1,850-2,200mm), thickness (A, B, E, BA, and EB flutes), and quality.

The other department prints and converts the sheets, either in- or off-line. For in-line printing, slitting, cutting, folding, and gluing, the company uses flexo top and bottom printers from Emba and Martin respectively. For off-line production, a four-color Deritend flexo top printer and a stand-alone rotary die-cutter are in use. The department also has three flatbed die-cutters (supplier is no longer in business).

"The advantage of working off-line," says Da Silva, "is that the press speed is not limited by the slower conversion speed [the maximum speed of the Deritend press is 13,000 sheets/hr, whereas a flatbed die-cutter can operate at a maximum of 6,500 sheets/hr]. Furthermore, printing and cutting are two different specialties. The die-cutting operators are not confronted with printing problems, because the printers have already removed any misprints prior to the die-cutting stage. Naturally, this is not the case when working in-line. Although off-line printing requires more manpower and in-between storage of the printed material, we still achieve a higher speed and better quality."

Controlling Production Conditions
"Corrugated board is a very practical packaging material," says Da Silva. "In terms of price and weight, virtually no other material can compete with its strength and stiffness. However, paper is a natural product and is always changing due to the humidity. We use heaters to keep the moisture of the paper between 8 and 11 percent. If the moisture is below 8 percent, this may cause problems when die-cutting, because the material may tear. If the material is too damp, it may create compression and printing problems. The application of glue is measured digitally—continuously—so we can act immediately when the tolerance is exceeded.

"Corrugated board is not flat by nature, so it needs to be ironed several times. Printing on corrugated board is rather difficult, because the underground virtually consists of air. In comparison, containerboard has a solid underground and is, therefore, much easier to print."

He continues, "Because we need to have maximum control over all production conditions to guarantee the quality, we have selected suppliers carefully so [their equipment] can help us control those conditions. We use photopolymer printing plates from Miller Graphics, water-based flexo inks from Manders Premier, and Ultracell anilox rolls from Apex."

The folding boxes produced in Eindhoven are mostly white, brown, or gray, yet print quality plays an important role because the boxes need to stand out on shelves in shops, canteens, and supermarkets to attract the consumer's attention. Anilox rolls are key tools to achieve a high print quality, says Da Silva. To maintain an optimum ink volume, it is important to check the anilox rolls regularly for wear, damage, and ink contamination. Cells clogged with dried ink will have a different shape and, consequently, a different ink volume. This influences the print quality.

Another factor that influences the print quality is the hydrophobic tendency of the anilox roll, says Da Silva. "The ceramic coating of Ultracell anilox rolls is homogeneous and compact with a non-wetting tendency and a low porosity. This results in a high surface tension and, thus, an improved release coefficient. The effect can be compared to drops of water standing out on a well-waxed car. Because of this effect, the ink leaves the cells of the anilox roll more easily. Such rolls can be cleaned more easily and also have a higher resistance to aggressive cleaners."

Managing the Anilox Rolls
What is particularly important to Assi-Doman is the correct anilox screen count (the number of lines per centimeter) in combination with the correct ink volume. Da Silva explains that AssiDoman prints heavy full tone, coarse text, and process, for which the company needs an ink volume between 8 and 14 cc per sq m (cm3/m2). "We have an agreement with Apex," he says, "whereby they measure the ink volume of all our anilox rolls on a quarterly basis."

For this, Apex uses a Ravol liquid volume tester. According to Da Silva, a specific quantity of liquid is injected onto the anilox roll, then spread with a blade over as many cells as possible. An impression of the resulting spot is made on a sheet of paper. With a device, the periphery of the spot is traced, and the spot surface is read directly off the LCD screen of the device.

By dividing the liquid volume by the measured area of the spot, an accurate anilox screen volume in cm3/m2 is obtained. The ink volume is measured in three places: in the middle of the roll, at the operator side, and at the drive side. After each measurement, the results are discussed. If the ink volume deviates from the required cm3/m2, Assi-Doman makes the decision to either replace or clean the anilox rolls based on advice from Apex.

Da Silva explains, "We can only work this way with suppliers we trust and who have extensive experience and know-how. Our experience with Apex is that they supply high quality products and offer a good service. In emergencies, they are always there to help, and they are a one-stop source of supply."

Keeping the Rolls Clean
Cleanliness is particularly important for those components that directly influence the print quality. Therefore, all anilox rolls are cleaned after each print job. AssiDoman uses the biodegradable BioClean cleaning liquids from Apex, because cleaning with water does not give the required results, according to Da Silva. "Not only does water require more cleaning time, operators also need too much water to clean the rolls properly. This results in large quantities of slightly polluted water. Although the water is polluted more severely when using cleaners, less water is needed. Overall, this is more environmentally friendly and more economical, since water needs to be processed regardless of the degree of pollution."

At the Eindhoven plant, Apex provides a periodical cleaning service for which it uses its mobile, on-press BioJet cleaning system. Says Da Silva, "Clean anilox rolls are extremely important to us. This preventive maintenance arrangement keeps our presses running smoothly and effectively and helps us to guarantee the continuity of quality."

Striving for Perfection
AssiDoman not only wants to supply high quality products, it also wants to be a reliable partner for its customers in every way, including just-in-time delivery. To achieve this, the entire organization is tightly structured and certified according to both ISO-9001 and ISO-9002 standards. The company measures its performance every week, says Da Silva, and close to 100% of the products are delivered on time.

For economic reasons, it is best to keep stock to a minimum. For some customers, AssiDoman keeps its products in stock and delivers just-in-time according to a pre-established schedule, taking into account seasonal influences.

A similar system has been developed by AssiDoman and Apex, whereby the latter keeps finished and semi-finished anilox rolls in stock at its headquarters to shorten the delivery time and to be able to help out immediately in emergencies.

Da Silva adds that AssiDoman's partnership with Apex extends even further: Recently, some 20 printers and operators received training on printing problems at the Apex premises.

Obviously, this is a partnership that works across the board.
Supplier Information
Apex Europe B.V. Hapert, the Netherlands; +31-497-361111

Peters Maschinenfabrik, Hamburg, Germany; +49-40-853-000

Emba Machinery AB, Orebro, Sweden; +46-19-300-500

Martin, Villeurbanne-Cedex, France; +33-4-72-14-7474

Deritend Engineering, Birmingham, England; +44-0121-706-6271

Miller Graphics, Haverhill-Suffolk, U.K.; +44-1440-703001

Manders Premiere Inc., Wolverhampton, U.K.; +44(0)1902-871028

Following the closure of its plant in Cumbernauld, Scotland, AssiDoman decided to relocate its (Pound Sterling) 1 million SHS Mark II Legend Supergraphics printer and rotary die-cutter to its plant in Lucca, Italy. The custom-designed Legend, accurate to 0.25 mm, produces laminated printing for retail packaging. As the original equipment manufacturer, SHS was put in charge of the three-month-long relocation project.

A team comprising five SHS personnel was involved in the relocation, which included planning and coordinating land and sea transportation and customs documentation and administration. The equipment, which consisted of seven main units and ancillaries, was moved on 11 lorries made up of 8 low-loaders and 3 trailers.

A partial redesign of the factory floor was necessary to ensure the equipment would fit into its new surroundings, and the Legend software was upgraded to ensure Y2K compliancy.