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Static Control



Small as they are, positive and negative ions can have a significant impact on the outcome of a print job as well as on the safety of workers.



Published November 28, 2005
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Static Control

Small as they are, positive and negative ions can have a significant impact on the outcome of a print job as well as on the safety of workers.

By Michelle Sartor

Most people have a vague idea of what static electricity is. They have probably gotten a shock at some point or had hair stand on end. Although these are minor inconveniences in everyday life, static can be a major problem for the narrow web printing industry. Having a better understanding of static and how to control it is beneficial to printers and can save them time, materials, money, and aggravation in the long run.


The Ion 360 ionizing rod, offered by Stopstatic.com, in operation on a press
The causes of static electricity are better understood if you know the definition. According to Sean Fremon of Cole Static Control Inc., Akron, OH, USA, “Static is the excess or deficit of ions on a surface.” There are positive and negative ions. When an object contains more positive ions, it has a positive charge. When there are more negative ions, the object has a negative charge.

Static is caused by friction, separation and temperature change. In the narrow web market, friction and separation are the most common causes of static. Bill Larkin, president of Stopstatic.com, a division of Alpha Innovation Inc., Marblehead, MA, USA, says, “Static electricity is generated usually when dissimilar materials make contact and separate.” When printing labels, this could happen during winding or unwinding of the roll. As the materials separate and rejoin, electrons are exchanged. The material that gains the electrons gets a negative charge, and the material that loses the electrons is left with a positive charge.

The presence of static electricity during the printing process can cause several problems for label printers. One major problem is web contamination. If the web acquires a static charge, it will try to get back to neutral, thus attracting material with the opposite charge. For example, says Fremon, plastic film tends to hold a negative charge. Therefore, the film will tend to pull in anything with a positive charge. Paper materials, he adds, tend to hold a positive charge. Throughout a plant there are boxes, wood and other paper based objects that can readily contaminate the web.

According to Larkin, “If the imbalanced field gets strong enough (greater than 3,000 volts), it begins to attract dust and dirt from the air and nearby surfaces, such as the floor.” Dust particles attracted to a charged web can create marks on the finished printed product.

Operator shock is another problem caused by static electricity. Larkin says shocks are made when the charge is above 10,000 volts. Although most times the shock itself is harmless to the operator, he or she could do some damage by recoiling from it. Also at the 10,000-volt mark, surface damage can occur. “Static discharges can damage surface coatings because of the heat of the electrical discharge,” according to Larkin.

Product damage is currently a big issue with static, especially with regard to radio frequency identification (RFID) labels. RFID products are sensitive to static and will not function correctly if exposed to voltage that is too high. Larkin says that if there is a charge on the RFID labels, a damaging electrostatic discharge (ESD) can occur when the labels come in contact with the metal rollers. (ESD occurs when a charge is transferred from one object to another, such as when an object is grounded.)

Jay Perry, Simco Industrial Static Control, Hatfield, PA, USA, explains another issue: Static charges are cumulative in nature.  “The surface charge starts out at a low voltage, but as the web goes over more rollers, the voltage goes up,” he says. Therefore, the charge toward the end of the process will be greater than at the beginning.

Something else to keep in mind is that grounding will not always eliminate static problems for label printers. Larkin explains: “Grounding works for conductors such as metal, carbon or people. But, by definition, an insulator cannot be grounded. The surface storage of electric charge on a plastic does not conduct and cannot be grounded.”

What to do

Though these are all challenging situations, there is help for label printers. There are a variety of products on the market to control static and alleviate the problems caused by it. The two main types of static control devices are passive and active. Passive control systems include tinsel, brushes and static string. These are the cheapest forms of static control and are placed right at the web. Matthew Fyffe, Meech Static Eliminators USA, Norton, OH, USA, says that the passive devices cost about $100. This affordability makes them popular. Larkin says, “Everybody uses copper tinsel in converting.”


Ion Virtual AC line of static neutralizers offered by Ion Industrial
According to Larkin, modern day copper tinsel contains microfibers that cannot be seen, while brushes contain conductive fibers to decrease static. Static string is useful when printing from roll to sheet. If you lay static string across a stack of finished product, it will remove static and keep the sheets from sticking together. Larkin says label printers have the most difficulty with static when printing from roll to sheet. Stopstatic.com offers a variety of passive devices, including its own elasticized static string, which is useful since it can be moved out of the way and then snapped back into the desired position without damaging the string.

Although passive control devices reduce the charge on the press, they will never eliminate it. Perry says the disadvantage of a passive control system is that it can only reduce the surface charge to its threshold voltage, and at that point it no longer works to reduce the charge further.


The 915 AC static neutralizer from Meech Static Eliminators USA
Active control devices, on the other hand, work using consistent corona discharge and are continuously working toward a voltage of zero. Perry explains that active ionization devices use corona discharge, which results from applying a high voltage across a very sharp emitter point, to stress the ambient air molecules and create the positive and negative ions required to neutralize static charges. Larkin says that when a charged web passes by the newly created ions, it attracts its opposite charge, neutralizing itself. The excess charge goes to ground. (Larkin points out that all systems are grounded.)

There are two main types of active devices: AC and pulsed DC technology. According to Fyffe, the AC devices are placed over the web itself, 1" to 6" away, just prior to the problem area. Pulsed DC devices allow for greater ranges and are usually used on winders. Their range is 6" to 36". AC devices have a fixed ion output and use air to assist with distribution. Pulsed DC devices, on the other hand, have adjustable ion output levels and do not use air in delivery.

Active devices come in a variety of forms: ionizing bars, guns, blowers, and nozzles. Ionizing bars, or rods, remove static electricity on the web in a paper or film converting application. The bar is placed close to the web and will not cause operator shocks. With ionizing guns, a concentrated flow of ionized air is shot out of the device, making the target electrically neutral.

Ionizing blowers provide a continuous stream of static-neutralizing ions to protect sensitive materials against ESD. They are used for larger areas since they contain electrical fans that project the ionized air farther away from the source. They enhance cleanliness by neutralizing charges that attract and hold particles on walls, tabletops and other surfaces. With ionizing nozzles, the ionized air is more directly distributed to specific areas. The nozzles operate on compressed air and can get ionized air into hard to reach places.

According to Mark Blitshteyn of Ion Industrial, Windsor Locks, CT, USA, “Air ionizers generate air ions of positive and negative polarity to neutralize static charges on the web. Installations at the unwind, rewind and after the corona treater are definitely a must. Installations after every print station are optional, but recommended.”

Fyffe says that active static neutralizers can cost between $500 and $2,000 per system depending on the size. He says a feedback system, which reads residual effects and adjusts the ions generated based on the findings, costs $2,000 to $3,000. Meech offers the new 986 DC Feedback System, which consists of a sensor bar and feedback controller that works in conjunction with the Meech 977v3 Pulsed DC controller and 976 ionizing bar. According to Fyffe, the type and sophistication of the static neutralizer depends on how high the converting company’s quality specifications are.

Cole Static Control, Ion Industrial, Meech Static Eliminators, Simco Industrial Static Control, and Stopstatic.com all sell static neutralizers. Simco and Ion Industrial offer only active static neutralizers while the others provide both active and passive devices.

Nuclear static neutralization is a third form of static control in which alpha particles, or polonium radiation, are emitted from foil and break the air down into positive and negative ions. Fyffe says nuclear devices are not very common in narrow web and are used more often with electronics and for explosion risk areas.

Controversy

According to Larkin, there is currently a controversy surrounding RFID labels and how to eliminate the problem of static during their production. He says some people insist that static elimination equipment alone will remedy the static problem with the static-sensitive labels. Larkin is not part of this school of thought, however.

“The use of static eliminators alone is impractical,” he declares, “because non-antistatic materials carrying RFIDs can charge up again immediately, and as an RFID leaves contact with a metal roller it can discharge back through the device. This ESD occurs much faster than any ionizer can eliminate it.”

His suggestion is to prevent an ESD from occurring. Since RFID labels get damaged when an ESD occurs on metal rollers, Larkin says printers can cover the labels with lamination that will not pick up a charge or cover the roller with a static dissipater. He says Stopstatic.com is working to develop materials that are permanently static dissipative and can be used to eliminate ESD.

Blitshteyn says that the Ion Virtual AC line of static neutralizers, available through Ion Industrial, is a good tool for RFID label inserters. He says it “offers modular design that allows static neutralizing bars to be connected in a daisy-chain configuration to a single power supply with monitoring circuitry. This arrangement is ideal for narrow web presses, and especially for RFID label inserters where as many as 10 static neutralizers are required.” He says the device is efficient, reliable and one of the most economical.

Web cleaners

Web cleaners should also include static eliminating components because static electricity causes dust attraction. According to Perry, Simco manufactures vacuum web and sheet cleaning equipment that dislodge, neutralize and remove particles that are on the surface of the web while also neutralizing any surface charges on the web before it exits the cleaner.

The company also offers contact cleaning equipment, which is able to clean away very small particles, down to one micron in size. (To put that in perspective, Perry says the cross section of an average human hair is 100 microns and particles smaller than 50 microns cannot be seen with the naked eye.)

Wandres Corp., Ann Arbor, MI, USA, sells web cleaners using the Ingromat system. In this process, a microscopic amount of antistatic cleaning fluid (Ingromat fluid) is put on the surface of the cleaner’s brushes. In addition to eliminating dirt and dust particles, the fluid neutralizes the charge of the web’s surface, removing static. According to Justin Elsley, the web cleaners cost $17,000 to $18,000 for machines between 16" and 18" wide. He says the cleaners are placed directly before the first print station.

Humidity

Humidity is a factor that greatly affects the creation of static. The lower the humidity, the more static will be produced. According to Kit Vernon, who works with Husson Inc., Sturtevant, WI, USA, the ideal conditions for air in a printing plant are 68° to 72°F, and 45 to 60 percent relative humidity (RH). Vernon says that if you heat air that is 10°F with 50 percent RH to 70°F, you will be left with between eight and 10 percent RH. That level is often too low. Vernon says, “Most plants have problems with static at 30 to 35 percent relative humidity.”

To combat the dry air and prevent static problems, printers can buy engineered humidification systems. These systems are typically placed at ceiling height and release a fine mist of small water droplets. Vernon says the droplets are so small that one would not be able to feel the water.

According to Vernon, it is most common with the humidification systems to divide the plant into zones and determine the desired humidity level for each area. Each zone contains a humidity meter that contacts a programmable controller if the RH level goes below the desired amount. The controller then makes the machine send out the mist to raise the RH level.

Husson sells engineered humidification systems from ML Systems, a Danish company. The ML models use fans for a more unified distribution of the mist. According to Vernon, most engineered humidification systems do not contain fans. He says the humidification systems without fans work because moisture is drawn to the driest area. Those systems release water droplets into the air and the drier areas of the plant suck in more of the moisture. Vernon says using a fan just makes the process faster, more uniform and more efficient.

Humidification systems can be used in conjunction with static neutralizers. Vernon says many plants contain both devices. He points out, however, that problems like shrinking or wrinkling of web material could have causes other than static on press, and static neutralizers will not necessarily work to correct the problems. Vernon believes that the humidification systems can remedy many of the issues. He says, “You don’t have much trouble with static electricity when the relative humidity is good.”

When static is desired

Although static can cause many problems on press, there are certain times when a charge would be beneficial. One instance would be if the press operator wanted to pin materials together, such as film and foil. Another would be if a printer wanted to laminateor interweave web material into tight layers. Blitshteyn gives two other examples: “A product is to contain a 2" by 3" thin coupon that a recipient of the product is expected to use. Rather than gluing this single piece, static could hold the coupon in place, saving the cost of procuring an adhesive-backed coupon or adding glue prior to placing the coupon in place. Another example would be holding in place a clear window film prior to UV application to secure it.”


Ion Industrial charging generators, models 7220 and 7020
Charge generators are available to create desired static. According to Blitshteyn, “The charging generator can be installed on the press machine frame and the charging applicator should be installed precisely at the point a patch is first in register with the carrier web. The system works by precisely charging the surface of the coupon with air ions of one polarity. The result is a coupon that now clings to the surface of the web.”

Charge generators work in different ways. Blitshteyn says, “Ion Industrial charging generator models 7020 and 7220 can operate in two modes: the constant voltage mode standard for most other generators in the market and the constant current mode, which provides more consistent pinning power regardless of changes in ambient conditions or contamination of ionizing electrodes or variations in the material’s properties.”

The bottom line

As quality expectations increase, static control becomes more important for the narrow web industry. Eliminating unwanted static electricity on press can not only decrease the amount of operator shocks, but also decrease the amount of dirt and dust on the web and increase the quality of the finished product. Employing charge generators to use charged surfaces as an advantage can help simplify certain print jobs.

And with the ever increasing quality standards in the industry, as Perry says, “Static control is becoming more of a requirement.”



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