Spotlight on Static Electricity

Static electricity problems during printing production are very common, leading to lost production, print defects and increased rejects, and a decrease in profit margins.

Substrates—such as paper, plastic, and textiles—are electrically balanced, containing the same amount of positive and negative charges. Friction can upset the balance, and the material becomes electrically charged. That static charge causes a host of problems, beginning with the attraction of dust to the substrate’s surface.

“For printing fonts as small as pharmaceutical instructions to large wide-format poster size pieces, the static electricity on the print media will often cause contaminants from the air to be attracted to the printed material’s surface,” explained Terrance Clark, TAKK Industries technical sales manager.

The much desired end result of good quality print isn’t possible when ink is applied onto a dusty or dirt laden surface.

“Additionally the static field on the printing surface can cause the ink to track or feather out the ink reducing the sharpness of the printed characters or images creating a fuzzy appearance,” Clark added.

Another common and undesirable effect of static electricity is for the printed material to stick to itself or rolls and guides, causing miss-feeds, jams, or jogging issues. Issues can occur during infeed and/or delivery.

Static charge is also an issue for employees, which at the very least will be an unpleasant experience for the employee, and at the very worst, can cause serious injury.  

Digital Delivers More Charge

In digital and wide-format printing environments, static is an acute challenge. The increased use of treated plastic substrates—such as styrene, polyvinyl chloride (PVC), polycarbonate and various types of foam boards—are treated with high-voltage corona to improve their printability, noted Bill Larkin, founder, Alpha Innovation, Inc. With this high static charge, the dust issue is elevated, along with printing complications such as clogged nozzles or overspray.

“We get constant calls about wide-format printers with difficult static issues,” acknowledged Larkin. Beside the substrate causing issues, digital printing devices impart a lot of static into sheets, due to the high heat used during imaging.

If a charge imbalance between substrate and ink develops, subsequent printing defects due to attraction and repulsion follow. Much like a magnet, ink particles are attracted to the charged areas of the substrate, deflecting the ink particles from their intended path.

Depending on where and in which stage the static charge occurs, you’ll have either sheets sticking to sheets or sheets sticking to machine parts. Either scenario presents problems for the wide-format print shop.

To eliminate static and the accompanying dust within the printing environment requires the use of a humidification system or, a mechanical device that removes static from the paper.

TAKK Industries offers a broad range of static elimination solutions, that includes both simple to use passive (no-power needed) static eliminators such as anti-static flex cord, tinsel, and brushes and best in class electronic powered static eliminators.

“Within our electronic offering is our high performance workhorse Model 400T Series bars that can be used with or without air assist,” explained Clark. “The basic Model 400T is highly effective at removing static form the media. The air assist Model 400T Air Bar removes dust and contaminate once attracted to the media. And for more robust dust removal, we offer the Model 400T Ion-Jet Super Air Knife static eliminator to remove contaminates before printing.”

Proper Humidity Controls Static

Proper humidity levels in offset prepress and pressroom areas, as well in digital printing production areas, are necessary for optimum equipment performance, print quality, and to keep dust down in the room, explained Andrew Douglas, president of PriscoTech Products.

Prisco is the sole distributor of Kersten anti-static control systems in the US and also has a full-line of PriscoTech humidification systems for pressroom and prepress areas.

Lack of humidity is a big issue for digital printers, noted Douglas. Within the printing facility, the accepted humidity is about 45 to 50 percent (some experts stretch it to 40 to 60 percent) relative humidity.

Dry air causes paper to lose its natural moisture, so it risks picking up static electricity resulting in wrinkling, losing register, and causing paper feed jams, reported Douglas. If the relative humidity is at around that 45 to 50 percent mark, it reduces the possibility of static charge. 

Keeping the humidity at an accepted level keeps down the dust, and is also necessary for problem-free media feeding.

Prisco’s line of humidification systems differ based on size of the room. Its modular concept consists of several different misting head options combined with a high-pressure water pump and ICC controller for a variety of configuration possibilities. Water is atomized into micro-sized particles that are absorbed quickly into the air, to ensure humidity control.  

The systems range from the AquaMist, which has one misting nozzle for up to 1,000 sqft of coverage; to the SpaceMist 125, with 10 evenly spaced misting nozzles to provide humidity up to a 3,600 sqft area.

“We analyze customer’s applications to determine their need and can build a system accordingly to what is required,” noted Douglas.

Kersten static elimination systems for the machinery blow ionized air to the surface of the charged product to eliminate static and restore the electrical balance.

The static may give serious problems at the infeed due to incorrect feeding or doubled sheets, slurring in print units, and poor stacking at the delivery.

Blowing ionized air into signatures the paper helps eliminate these problems.

The systems range in price depending on the application and machinery. “We customize that for presses as well,” said Douglas.

To fight the issue of static electricity, press operators try slowing down their presses to a very slow speed. If the press is running fast at rated speed, there is more friction and therefore more static.

If the printer uses a static elimination system or humidifier, the operator can run the press at speed.

Pulling The Strings

StopStatic.com, a division of Alpha Innovation, is the manufacturer of StaticString, an anti-static cord that was first patented in late 1997.

Static string is one of the largest selling cords in the world, replacing copper tinsel, said Larkin.

When a sheet is laying flat or in a stack; it’s difficult to get the static that is in between the layers.

If static is present, printers have problems feeding sheets; they end up with a whole bunch that won’t go in and then get doubles, says Larkin. When a double sheet is detected, it stops the printing device.

If you don't’ use a good static eliminator on that sheet, then you can’t feed them into folder or laminator, said Larkin.

Thе Static String anti static cord іѕ an ion wire-it’s the thinnest little wire, said Larkin. “It’s mаdе up οf tіnу, conductive microfibers thаt you can’t even see because they are so small,” he said.  The microfibers cause thе static charge tο ionize and go tο ground.

StaticString іѕ designed tο fit іn tight spaces; on a folder or a machine where there is a bed, the wire is placed underneath the paper; so it travels across with the wire under it, eliminating the static charge.

The kit is very affordable, says Larkin, costing $139; for about 100 feet of static elimination cords.

A wide-format kit is also available that includes StaticElastic, magnets for grounding, and Staticure Spray & Static Tape.

“Static by its very nature will cling to the nearest object; we developed a piece of tape that they can tape to the bed to attract the static,” Larkin explained.  Staticure Spray stops static electricity on contact.

StaticElastic removes static from flexible and rigid materials before they enter the printhead area. It looks like a bungee cord and attaches to the printer with magnets that ground it, said Larkin.

By attaching StaticElastic across a flatbed printer’s belt feed mechanism, charged substrates are neutralized before entering the printer. These can also be placed where the material exits the printer to minimize painful shocks to operators.  

The StaticElastic may be placed across the conveyer, under the media, and grounded to the metal of the machine, removing static from both sides of the substrate.